Oof. 

Rising gas prices are starting to hit airlines. On Wednesday, May 30, airline stocks fell as oil topped $67 a barrel. Higher fuel prices could affect the ability for airlines to increase capacity in the short term, pointed out Delta Airlines at a conference on Wednesday.

The airlines index, which is shown below, shows how volatile the market has been for airline investors. In effect, the index has gone straight down since late February. 

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When the market closed on Wednesday, American Airlines Group Inc. (AAL) - Get American Airlines Group, Inc. Report  was down nearly 1%, Delta Air Lines Inc. (DAL) - Get Delta Air Lines, Inc. Report was up slightly, JetBlue Airways Corp. (JBLU) - Get JetBlue Airways Corporation Report was down more than 1%, and Southwest Airlines Co. (LUV) - Get Southwest Airlines Co. Report was down 0.3%.