Americans work notoriously long hours compared to most of the developed world. 

But some states are busier than others. 

To find out which state's residents put in the longest hours, Business Insider took a decade's worth of data (2003 to 2013) from the American Time Use Survey and calculated the length of the average workday of survey respondents who reported spending any time at work, in all 50 US states. 

Here are the ones the work the hardest:

North Dakota: 8 hours, 2 minutes per day

New Mexico: 7 hours, 49 minutes per day

West Virginia: 7 hours, 49 minutes per day

Hawaii: 7 hours, 45 minutes per day

Georgia: 7 hours, 43 minutes per day

Alabama: 7 hours, 42 minutes per day

Virginia: 7 hours, 41 minutes per day

Wyoming: 7 hours, 41 minutes per day

Arkansas: 7 hours, 40 minutes per day

Texas: 7 hours, 37 minutes per day

Perhaps surprisingly, North Dakota tops the list.

As The Washington Post has pointed out, a few factors make the average workdays in this upper Midwestern state especially long: 

North Dakota is the center of the American shale oil boom, creating tons of wealth and work. Oil jobs starting at $100,000 have created boomtowns across the state.

Loads of (mostly male) oil workers have flocked to North Dakota, where they work super long hours before retiring in "man camps" in the evening. 

At less than 700,000 people, North Dakota has the third-lowest population of US states, making the average easier to swing. 

But all that work doesn't seem to have taken a toll on well-being. Interestingly, North Dakota is also the happiest state in America. 

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SEE ALSO: What Life Is Like In North Dakota, America's New Happiest State