Airline stocks are rising in afternoon trading and could break a losing streak caused by investors' concern that cheaper oil has tricked the carriers into growing too quickly.

In trading Wednesday afternoon, the Arca index of airline stocks was up 2 percent after six straight days of losing. Shares of most major carriers were up too.

Investors are worried about slippage in a key financial figure that suggests airlines are losing their power to raise fares because of too many added flights. Several airlines expect that revenue for each seat flown one mile will be lower in the second quarter than it was a year ago.

For a couple years, airlines have tightly controlled the supply of seats — the average flight is now more than 80 percent full — allowing the carriers to charge higher fares. But cheaper jet fuel may have encouraged some airlines to add flights faster than the growth in travel demand — capacity is up about 4 percent from this time last year.

On top of that, oil prices have crept higher since March, so airlines won't get the full windfall that they once expected from cheaper fuel.

Airline stocks started sliding last week after Southwest announced another increase in its planned expansion for 2015, and after Parker said that American would cut prices to match moves by discount carriers.

Wolfe Research analyst Hunter Keay said investors gave Southwest a hard time for growing in Dallas. "The issue isn't growth there," he said in a note to investors, "but a lack of cuts elsewhere" to offset growth in Dallas.

Keay lowered his forecast of earnings at seven airlines including the big four — American, United, Delta and Southwest — through 2017. UBS analyst Darryl Genovesi cut his 2015 profit forecasts for all but United.

All four stocks fell sharply on Tuesday, the first trading day after a three-day holiday weekend, but they were recovering in afternoon trading Wednesday.

Shares of American Airlines Group Inc. were up 77 cents, or 1.9 percent, to $42.325; Delta Air Lines Inc. was up 69 cents, or 1.7 percent, at $42.54; United Continental Holdings Inc. gained $1.73, or 3.3 percent, to $53.65; and Southwest Airlines Co. added 88 cents, or 2.4 percent, to $36.88.

At their closing prices on Tuesday, all four were down sharply from their 2015 high prices — ranging from Delta off 18 percent to United down 30 percent. That contrasted with 2014, a banner year in which Southwest and American shares more than doubled in price and others weren't far behind.