Aqui un listado que he encontrado con las limitaciones en algunos paises
Austria - No restrictions in fpe but limit on caliber (FAC req for .25 and above)
Australia- FAC required for everything and anything.
Belgium - No restrictions on rifles
Brazil - No restrictions
Bulgaria - No restrictions
Canada - 500 fps limit without a PAL
Cyprus - .177 only (No information on energy levels at this time)
Czech republic - 12 fpe (16 Joules)
Denmark - No restrictions, but soon will have restrictions imposed due a change in the legislation.
Estonia - No limits in .177, .22 and larger cal FAC required. No hunting with air gun
Finland - No restrictions .22 is fac use only 150m+ from a road or dwelling, no licence required to own .177 can be shot in the garden where safe. No hunting with air guns.
France - 7.5 fpe (10 Joules)
Germany - 6 fpe (7.5 Joules)
Greece - No power or Calibre restriction, Silencers and Scopes are banned by law. Hunting is not allowed.
Holland - No restrictions - NO look a like's
Hong Kong - Max power of 2 Joules without an FAC
Hungary - 6 fpe (7.5 Joules)
Italy - 6 fpe (7.5 Joules) must be over 18 to buy, over 10 to shoot it with presence of a parent; >6 fpe you need a f.a.c. and you've to declare the purchase to the police. NO Hunting.
Japan - Airguns firing metallic projectiles are considered firearms and require a license for specified use.
Latvia - 12 Joules
Lithuania - 7.5 Joules (NO hunting allowed)
Luxembourg - FAC required for everything and anything.
Malta - FAC required for everything and anything.
New Zealand - Recent restriction, As at the 15th October 2010, the amendment to the Arms Order 1984 (restricted weapons and specially dangerous airguns) will class any 'Pre - Charged Pneumatic (PCP)' Air Rifles (excluding PCP airguns used in airsoft and paintball sports), will be classed as 'Specially Dangerous Airguns', and will require the owner to hold a current 'Firearms Licence'. FAL must be obtained by 14th Jan 2011.
Northen Ireland & EIRE - Airguns or CO2 guns that are in excess of one (1) Joule (0.737 ft/lbf) require to be held on an FAC.
Norway - No restrictions
Philippines - No restrictions but all airguns must be registered at the local police office. No license required (formality)
Poland - 12.5 fpe (17 Joules) (NO hunting allowed) >17 Joules allowed if gun is registered with police (Formality)
Portugal - .177 or .22 Chuck Norris velocity of 1181 fps Hunting not allowed
Romania - ?

Russia - 6 fpe (7.5 Joules) (Unsure of this one)
Slovak republic - 11 fpe (15 Joules)
Slovenia - ?
South Africa - Below .22 No restrictions. .22 and above - Chuck Norris 7.5J No 'hunting'* with airguns, but pest control allowed, no shooting in built up areas. (exceptions for Big Bore when having a huntinglicense - hunting on larger game)
Switzerland - No restrictions (Over 18 to purchase) On birds are legal quarry.

Spain - 18 fpe (24.5 Joules)
Sweden - 7.5 fpe (10 Joules (same for rifles and pistols) semi- or full auto airguns: 3 Joules.)
Turkey - No restrictions
UK - 12 fpe (16 Joules)
USA - No restrictions (Except New Jersey, Delaware, Massachusetts and Michigan) Also numerous restrictions when within City Limits, varies state to state