All values are estimates and based on a prototypical 70 kg male, and energy expenditure is generally lower in women. Although the MET data used is from the most accurate source available, there are some obvious inaccuracies with some of the METs, for example the MET for surfing is the same as playing Frisbee and as any surfer will tell you, this is clearly not the case.
The activity calorie calculator will give you estimates of calories burned for the various exercises and activities.
References:
1. Ainsworth BE et al., Compendium of physical activities: classification of energy costs of human physical activities. Med Sci Sports Exerc. 1993 Jan;25(1):71-80. PMID: 8292105
2. Ainsworth BE et al., Compendium of physical activities: an update of activity codes and MET intensities. Med Sci Sports Exerc. 2000 Sep;32(9 Suppl):S498-504. PMID: 10993420
3. CDC