Oil Math that both J.R. Ewing and Michael Lewis Would Love

From the current issue of Bloomberg Businessweek regarding the winners and losers in the global oil bust:

"During the boom years, some shale producers spent $2 drilling for every $1 earned selling oil and gas, according to data compiled by Bloomberg, and they plugged the shortfall with debt.  Wall Street extended low-interest credit lines to junk-rated borrowers, which put up their oil and gas properties as collateral.  Producers tapped their bank lines to buy properties and drill wells.  When companies needed to pay off their loans, their bankers helped them sell equity and debt.  Investors, hungry for higher returns after years of low interest rates, snapped it all up."