The way energy companies are issuing debt, it feels like spring is in the air—the spring of 2014.

Back then, the industry was riding high on $100-a-barrel oil, and companies were selling mountains of debt to fund ambitious growth strategies. It was a time when "almost anybody could bring an energy deal, and almost everybody tried," said Scott Roberts, head of high-yield investments at Invesco Ltd. in Atlanta.

Then oil prices plunged, along with the fortunes of many borrowers. Crude hasn't approached $100 since, but it has stabilized around $50, and that has energy companies returning to credit markets at the fastest pace in three years. This time, companies like Transocean Ltd. are looking to refinance more than to expand. And they're finding pent-up investor demand that's bolstering prices and giving issuers incentive to come forward, Roberts said.