The NPD Group, sales-tracking statistical firm, has released the top 20 chart showing North America's best-selling computer games throughout 2009, and it's the Sims and World of Warcraft titles that proved most popular at retail.

Games from The Sims series are responsible for 5 of the top 20, while the online adventure game World of Warcraft accounts for four of them.

The original Sims game, top of the chart here, was in fact first released in the year 2000, with The Sims 2 following up in 2004 and The Sims 3 itself in 2009.

The games involve taking care of little computer people, building houses for them, and helping (or hindering) them in their daily lives. According to publisher Electronic Arts, the original game is the best-selling PC game of all time, having cleared over 100 million copies.

The company behind subscription-funded World of Warcraft, Blizzard Entertainment, also did extremely well for themselves, as they also made the four 'Battle Chest' compilations that are present here.

In contrast with video game sales, where 12 of the top 20 were rated 'E for Everyone' by the ESRB, the popular computer games were primarily aimed at those of teenage years or older.

Twelve titles carried a 'Teen' rating, six were 'Mature' ( Modern Warfare 2, Dragon Age: Origins, Starcraft, Dawn of War II, Left 4 Dead 2, Diablo), and only Mumbo Jumbo Assortment and Spore carried some sort of 'Everyone' denotation.

1. The Sims
2. World of Warcraft: Wrath of the Lich King expansion pack
3. The Sims 2: Double Deluxe
4. World of Warcraft: Battle Chest
5. Call of Duty: Modern Warfare 2
6. World of Warcraft
7. The Sims 3: World Adventures expansion pack
8. Spore
9. Dragon Age: Origins
10. Empire: Total War
11. The Sims 3: Collector's Edition
12. World of Warcraft: Burning Crusade expansion pack
13. Aion
14. The Sims 2: Apartment Life expansion pack
15. Starcraft: Battle Chest
16. Warhammer 40.000: Dawn of War II
17. Left 4 Dead 2
18. Mumbo Jumbo Assortment
19. Diablo: Battle Chest
20. Warcraft III: Battle Chest
Source: The NPD Group/Retail Tracking Service