The G-7 Nations:

The G7 is composed by the 7 developed wealthiest countries on Earth (as national net wealth) and by the 7 developed wealthiest countries on Earth by GDP,[2] and it remains active despite the creation of the G8.

Canada
France
Germany
Italy
Japan
United Kingdom
United States

The G-8 Nations:

The Group of Eight (G8) is a forum for the governments of seven leading industrialised democracies, plus Russia.

Canada
France
Germany
Italy
Japan
United Kingdom
United States
Russia
 
The G-20 Nations:
 
The G-20 or “group of twenty,” is a group of twenty of the most important economies on the planet. It includes 19 independent countries along with the European Union.

1. Argentina
2. Australia
3. Brazil
4. Canada
5. China
6. France (also a member of the EU)
7. Germany (also a member of the EU)
8. India
9. Indonesia
10. Italy (also a member of the EU)
11. Japan
12. Mexico
13. Russia
14. Saudi Arabia
15. South Africa
16. South Korea
17. Turkey (an applicant for the EU)
18. United Kingdom (also a member of the EU)
19. United States
20. European Union (members of the EU)