Workers with Raven Drilling line up pipe while drilling for oil in the Bakken shale formation outside Watford City, North Dakota.

U.S. oil production has topped 10 million barrels per day, approaching a record set in 1970, but many investors in the companies driving the shale oil revolution are still waiting for their payday.

Shale producers have raised and spent billions of dollars to produce more oil and gas, ending decades of declining output and redrawing the global energy trade map. But most U.S. shale producers have failed for years to turn a profit with the increased output, frustrating their financial backers.

Wall Street's patience ran out late last year as investors called for producers to shift more cash to dividends and share buybacks.

"'Give me some cash, please.' That's what investors have said," said Anoop Poddar, a partner at private equity firm Energy Ventures.

And yet such calls for payouts remain a debate in the industry as oil prices have recently creeped up to four-year highs. Investors demanding immediate returns could risk forcing firms to curb expansion that could have a higher long-term payoff if oil prices continue to rise.

For now, share prices of shale producers have yet to fully recover from the 2014 oil price collapse, when many investors took losses as hundreds of firms went bankrupt and those that survived struggled.

The energy sector has lagged the rally that took the broader stock market to record highs. The S&P 500 Energy Index remains nearly a third off its peak in mid-2014, when oil prices topped $100 a barrel. The broader S&P 500 index is up 39 percent during the same period.