Premium economy class, also known as elite economy class or economy plus class, is a travel class offered on some airlines. It is usually positioned between standard economy class and business class in terms of price, comfort, and available amenities. In 1991, EVA Air was the first to introduce Evergreen Class (later renamed Elite Class, and then to Premium Economy Class), becoming the first airline to offer this class of service. It can be said that in many ways, Premium Economy class has become a standard reflection of what Economy class was like several decades ago. In some countries, this class has emerged as a response from governments and companies requiring economy class for travel done by staff.
Air New Zealand's and Qantas' Premium Economy include amenities such as prioritized check-in, large customized seats (some for couples, others targeting solo travelers), seat pitch up to 41 inches (104 cm) with 50% more recline, premium meals, a self-service bar for drinks and snacks, a personal in-flight entertainment center with remote control, noise-cancelling headphones, choices in games and movies for children and adults, skin care products in the lavatory, and an amenities pouch containing items such as socks, sleep masks, earplugs, and toothbrushes.
At the other extreme, some airlines market extra legroom seats in Economy Class, with the same service and seat model, as an enhanced Economy class. For example, in the United States domestic market, airlines such as American, United, Delta, and JetBlue have an upgraded Economy class with 2–5 inches (5–13 cm) more leg room as the only difference; they market the class as Main Cabin Extra,Economy Plus, Comfort+, and Even More Space respectively, while other services such as ground services and food and beverage services are on par with their normal Economy Class.
Service codes used by airlines vary, but W is the most common code.
Examples of differences
Differences between Premium Economy class and Standard Economy class may include (varies by airline and country):
a separate section of the economy/coach cabin with more legroom (36–42" (91–106 cm) seat pitch), along with some form of leg rest,
improved in-flight entertainment features (larger screen, more options, included headphones, etc.)
dedicated cabin crew
smaller cabin size
better seats (often fewer seats per row, allowing seats to be wider, and to increase shoulder/elbow room, further ahead which gives less engine noise and faster unboarding)
at-seat laptop power
lounge access (for some airlines)
priority check in/security check/boarding
increased frequent flyer points
exclusive amenity kits
hot towel service
welcome drinks (juice or champagne)
upgraded meals and drinks
increased luggage allowance
better rebooking possibility
Some airlines may designate an entire economy class as premium, such as United p.s. on its transcontinental Boeing 757-200 premium service aircraft. In other airlines premium economy may be what used to be regular economy before more seats were added, or just the most attractive rows in the economy section. Premium Economy tickets also normally earn more mileage in an airline's frequent flyer program, attracting a bonus between Economy and Business. These upgrades tend to be more common on wide-body aircraft, such as the Boeing 747 and 777, and less common on narrow-body aircraft, such as the Boeing 737.
Aerolíneas Argentinas: Club Economy: Only on 737s and E190s. Replacing business class on all domestic flights and international flights under 4 hours. Offers similar benefits to business class, including lounge access.
Aeroméxico: Aeromexico Plus, now standard across the entire Boeing fleet. Offers 4" extra leg-room, 1.5" more recline and adjustable leather headrests. Includes priority check-in, baggage handling, boarding and deplaning, as well as extra mileage for frequent flyers.
Air Senegal : Premium Economy is offered on their Airbus A330-900, in a 2-3-2 configuration in contrast to 2-4-2 ( Economy ) and 1-2-1 (Business)
Air Canada: Premium Economy - on some International routes with new Boeing 777, Airbus A330-300 and on all Boeing 787 aircraft.
Air Caraïbes: La Classe Caraïbes (Long haul only. Offers 36" of pitch, more recline, a wider seat, a larger PTV and more)
Air China: Premium economy (only on A330-300s and 777-200s. Wider seat with at least 36" of pitch, nearly double recline and a PTV, plus more amenities. The new 747-8s and 787-9s will also offer Premium Economy)
Air France: Premium Economy. Offers SkyPriority, paid lounge access, improved meals (including stainless steel cutlery and real glass drinkware), a separate cabin featuring fixed shell seats with a 97 cm pitch and extra wide armrests.
Allegiant Air: Legroom Plus: Offers up to 4" more pitch. Giant Seats: Only on 757s. Bigger seats with at least 6" more pitch, similar to Spirit's Big Front Seats.
American Airlines: Main Cabin Extra  (offers a slightly wider seat only on the Boeing 777-300ER, 2" more recline and 4-6" more legroom but no other benefits). Premium Economy available on the entire long haul fleet. Premium Economy customers will also get two free checked bags, priority boarding, and enhanced food and drink service including free alcohol. This product will make American Airlines the first U.S. carrier to offer a four-cabin aircraft.
Condor: Condor Premium Economy offers more recline and 15 cm/6" more legroom on long haul flights in its Boeing 767-300 fleet, free spirits during meals, free amenity kits, free headsets and more. Short haul planes have the middle seat blocked off and no extra legroom or recline.
Delta Air Lines: Delta Comfort+ (Offers up to 36 inches of pitch, especially on planes with a pitch of either 32 or 33 inches in economy class) and free HBO programming. 50% more recline and free spirits are also offered on long-haul, transcontinental and international flights. Transcontinental flights between JFK and LAX/SEA/SFO also get 1 free premium snack and a free cold meal from Luvo, as well as a pre departure bottle of water and a sleep kit) 
Edelweiss Air: Economy Max: Long-haul only. Offers 15 cm/6" more pitch and 5 cm/2" more recline(94 cm/37" of pitch and 20 cm/8" of recline in lieu of 79 cm/31" of pitch and 15 cm/6" of recline in Economy), as well as free alcohol and an amenity kit.
El Al: Economy Space (Previously called Economy Plus) On 747s, 777s, 787s and 767s. Offers 4" more pitch (36" up from the usual 32"), 33% more recline, a footrest, priority ground service, a comfort kit, a bottle holder and more.
Finnair: Economy Comfort (Coming December 2014 to long haul aircraft. Offers 3-5" more seat pitch, comfier headrests, a comfort kit and better headphones)
Frontier Airlines: Stretch (first 4 rows and exit rows of Airbus offering a minimum of 36in pitch.)
Hawaiian Airlines: Extra Comfort (Airbus A330-200 and A321neo aircraft, comes with priority boarding, full 36 inches (91 cm) of legroom, complimentary on-demand in-seat entertainment, upgraded meal on international main meal only, comfort kit on international routes only, complimentary pillow and blanket on all domestic routes, souvenir pillow and blanket set on international routes only).
Iberia: Premium Economy on A340 and A330: Larger seat width/pitch, larger IFE screen, amenity kit, and priority check in/boarding.
JetBlue: Even More Space (offers a minimum seat pitch of 38", as well as both priority boarding and screening)
KLM: Europe Select (Only on inter-Europe itineraries, on B737-700/800/900 models) Economy Comfort (Long-haul only). Similar to Delta's Economy Comfort, offering similar seat pitch, and amenities, but with a larger recline advantage.
LATAM Chile: Premium Economy: Only on A320 series planes. Provides more legroom, width, and recline, plus the middle seat is blocked out to allow more space.
Scoot: Super/Stretch seats (Located in the 1st few rows and all bulkhead and exit rows in the economy cabin. Seats offer more width, 3-5" more pitch and on 787s adjustable headrests. These seats are distinguished be being a different color that the standard economy seats in light blue and Super/Stretch seats in dark blue.)
Singapore Airlines: Premium Economy class aboard all Airbus A350-900, Airbus A380-800 and refitted Boeing 777-300ER aircraft, serving to Europe and United States
Spicejet: Premium Economy (Located in the 1st 5 rows and exit rows of all 737s, featuring a 36" seat pitch, priority boarding and baggage handling and a larger baggage allowance, much like the SpiceMAX bundle)
Sunwing Airlines: Elite Plus: Offers at least 6" extra pitch, larger baggage allowance, and priority boarding, check-in and baggage handling.
TAM Airlines: Space Plus: Only on select 777s. Offers at least 36 inches of seat pitch and more recline.
Thomas Cook Airlines: Premium Class: Long haul only. Bigger seats with 35-36" of pitch, plus other services. Thomas Cook Airlines are no longer trading.
Ukraine International Airlines: Premium Economy (only on 767s. Offers 36-37" of pitch and a wider seat, plus priority ground service, better food options including a free glass of wine, and increased baggage allowance)
United Airlines: Premium Plus offers more seat recline, more seat width, extra legroom, alcoholic drinks, and better food options.
Vietnam Airlines: Economy Deluxe available on A350s and 787s on European, East Asia & Australia hauls
Virgin America: Main Cabin Select (not its own cabin - includes 12 bulkhead and emergency row seats on each plane)
Virgin Atlantic: Premium Economy. Virgin Atlantic also offers Economy Delight seats in Economy that have 3-4" more legroom.
Virgin Australia: Premium Economy. An Economy Plus section will be added to 777s starting late 2015.
Vistara: Premium Economy (in Airbus A320-200) seats have 3–6" longer pitch and recline further than in Economy class, Cold/Hot towel service, Welcome drinks, Specially curated menu with Two vegetarian and One Non-vegetarian meal option, Dedicated check in counters, Priority Boarding, Extra baggage Allowance and Priority baggage handling, Extra Club Vistara points. Vistara will also have Premium Economy class on its upcoming A321neos and 787-9s which are expected to join the Vistara fleet by 2020.
WestJet: Economy Plus: Located in the 1st 3 rows and exit rows, offering at least 36" of pitch, free food and drinks and priority boarding.
Some airlines no longer offer Premium economy:
Olympic Air: If passengers were traveling aboard a Bombardier Dash 8, the seat next to them could remain empty upon their request. This service was branded as "Premium Economy Class" and cost more than normal Economy Class. Moreover, they could use premium check-in facilities, if available, and were offered a welcome drink on board. Aircraft other than the Dash 8 didn't offer Premium Economy, but Business Class, which was discontinued immediately after the airline's buyout. Premium Economy was discontinued after the airline buyout too, because of its similarities to the business class of the company who bought Olympic Air, Aegean Airlines.
South African Airways: SAA never had a designated Premium Economy cabin, but the upper decks of their Boeing 747-400 aircraft featured Economy Class seats with 35 inches of legroom, compared to 31 inches in the main cabin. However, these seats were very exclusive, because they were mainly reserved for Voyager Platinum and Star Alliance Gold passengers. The Boeing 747-400s were retired from SAA's fleet in 2010, and the Premium Economy product was retired as well. One version of their A350 offers an Economy Plus section with 5" of extra seat pitch.