U.S. oil and gas drillers have cleaned up their balance sheets over the last year, but some analysts worry they are growing production at the expense of financial discipline.

Drillers look healthier today after slashing capital spending, putting dollars behind their most productive land and securing discounts from the companies that help them extract oil from their wells. But many are still spending beyond their means to hike output at a time when analysts are cutting their oil price forecasts.

Some analysts worry that some drillers could find themselves in a familiar and unwelcome situation: searching for funding to keep oil flowing.

That was the scenario one year into the oil price downturn, when CNBC analyzed two key measures of financial health in the oil patch — free cash flow and debt compared with earnings — for 44 drillers and found a sector outspending cash on hand and loaded to the hilt with debt.

Today, a recovery in earnings has helped drillers reduce relative debt levels that soared at the bottom of the oil market. And while many drillers are still spending more than they make, their cash flow has generally improved.