Americans work 50% more than the Germans, the French and the Italians. Americans may work more than Europeans because of domestic tax rates - there are lower tax rates in the US than in Europe, and hence working more pays off more in the US. In other words, working longer hours pays off more in the US than in Europe.

This study compares the working hours and life satisfaction of Americans and Europeans using the World Values Survey, Eurobarometer and General Social Survey.

The purpose is to explore the relationship between working hours and happiness in Europe and America. Is it possible that working more makes Americans happier than Europeans?

The findings suggest that Americans may be happier working more because they believe more than Europeans do that hard work is associated with success.

References:
Europeans Work to Live and Americans Live to Work (Who is Happy to Work More: Americans or Europeans?). Adam Okulicz-Kozaryn. Journal of Happiness Studies, 2010.