What's the deal with crude oil? The commodity is down about 4% midday Tuesday, but the decline has leveled off for several hours now.

Investors are bailing on the commodity because an OPEC production deal seems to be becoming more and more of a long shot now, TheStreet's Jim Cramer, co-manager of the Action Alerts PLUS portfolio, said from the floor of the New York Stock Exchange.

Oil has been going up based on rumors of this deal getting done, then down on reports that key players -- like Iran -- don't like the terms or that the deal is unlikely to be finalized.

Investors need to "be very careful," Cramer said, because oil-related stocks have rallied a great deal on the prospects of a deal getting done. No deal would equal lots of downside for these stocks.

Cramer said this is just day one of the declines. Should no deal materialize, more losses will come and that it's never wise to jump in on the first day of declines when it comes to the oil market.

At the time of publication, Cramer's Action Alerts PLUS had no position in companies mentioned.

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