BigInch:
Of course, there is no standard natural gas composition. I agree with you.
However, if you will look at the BP spreadsheet again and more carefully, you will see that it not only defines 1 BOE as 5,610 cubic feet of natural gas but it also defines 1 BOE as 5.8 x 106 BTU which is exactly the same as the U.S. IRS number that you quoted. That equates to an average natural gas heat content of 1036 Btu per cubic foot which is quite reasonable.
If the original poster (honerus) only wants an average conversion factor, he can use either your "approximately 6,000 cubic feet" or BP's "5610 cubic feet". They are both reasonable. If he wants an exact conversion factor for a specific natural gas, then he really should calculate it from the composition of his specific gas.
Milton Beychok
(Visit me at www.air-dispersion.com)
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