As the world awaits U.S. President Donald Trump's verdict on the 2015 Iran nuclear deal, climbing oil prices show that investors are expecting the worst.

Energy markets are indicating that the U.S. is likely to pull out of the accord and reimpose sanctions on Tehran, according to Dubai's largest bank, Emirates NBD.

The deal, officially called the Joint Comprehensive Plan of Action, lifted international sanctions against Iran in exchange for it curbing its nuclear program. Trump has referred to the agreement as the "worst deal ever," and he must decide by May 12 whether to reimpose sanctions or to grant the country a waiver.

"Anything that's slightly less than that — by which I mean he may delay his decision, or he may not impose the same amount of sanctions previously — I think markets would react favorably to that, given that markets are currently pricing in probably the worst-case scenario," Tim Fox, head of research and chief economist at Emirates NBD, told CNBC's "Capital Connection."