But oil and gas is a huge chunk of the extraction business, and the percentage depletion rules are more favorable for fossil fuels than for other things you might extract.

FORBES: Corporate Tax Reform and the Energy Sector

Canadian's oil and gas trusts typically pay out most of their cash flow (net income plus noncash charges like depletion) to unit holders.

FORBES: Out of Energy

"Considering the rapid depletion of the world's oil reserve, the heightened global interest in addressing greenhouse gas emissions and the geopolitical complications of global oil supply and demand, " a report by the U.S. Department of Energy concluded.

FORBES: Green Business