As others have said, there are only 8 seasons. The confusion comes from tv stations splitting up the 4 futurama movies and labeling them as season 6. And then splitting up the real season 6 and 7 and labeling them season 7-10.

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But the correct order is:

• Season 1 - as advertised
• Season 2 - as advertised
• Season 3 - as advertised
• Season 4 - as advertised
• Season 5 - as advertised
• Bender’s Big Score - split up and labeled as season 6
• Bender’s Game - split up and labeled as season 6
• The Beast with a Billion Backs - split up and labeled as season 6
• Into the Wild Green Yonder - split up and labeled as season 6
• Season 6 - split up and labeled as season 7 and 8
• Season 7 - split up and labeled as season 9 and 10
• Season 8 - labeled as season 11

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Source: TheTVDB