For four years, salesmen in Florida and Tennessee boiler rooms sold prospective investors on what they claimed were oil and natural gas projects “tailored for the conservator investor,” guaranteeing them “safe and consistent” annual returns of 15 percent to 55 percent that would ‘last for decades.’ “

Through companies called the Southern Energy Group, TennStar Energy and Black Gold Resources four men — two of them convicted criminals and two with troubled histories as broker-dealers — and the sales teams they oversaw secured more than $15 million from investors across the nation, federal prosecutors in Savannah say.