Renowned energy trader Mark Fisher is not parsing words when it comes to buying crude oil and natural gas — on Friday, he advised buying any dip in the commodities.

Crude futures have rallied about 90 percent since bottoming out earlier this year in the upper $20s, but remain well below their 2014 highs above $100 a barrel. They have more recently been bolstered as OPEC prepares to launch its first coordinated output limits in eight years in order to prop up prices.

This week, U.S. crude traded at a 15-month high near $52 a barrel.

Despite expectations that the OPEC deal will be difficult to enforce, Fisher said he believes oil will continue on a slow grind higher over the next 12 to 18 months.

"In my opinion, the most likely course is for the market to gradually establish a new base someplace in the $55 to $65 range barring some kind of geopolitical problem," he told CNBC's "Fast Money: Halftime Report."

Fisher is the founder and CEO of MBF Clearing, one of the leading energy-oriented introducing brokers.

As crude rallies, futures are up about 29 percent year to date. Last week, they struck a high going back to December 2014 of $3.36 per million British thermal units.

Fisher said he believes natural gas can hit $4 per million British thermal units in just a short time.

"It used to be that in natgas, every time the market rallied you could just close your eyes and sell it. I think those days are long over. I think now the time has come that you can basically buy every dip," he said.

The simultaneous rally in the U.S. dollar and crude oil lends further evidence that commodities are on the upswing, he said. A stronger greenback makes crude oil and other dollar-denominated commodities more expensive to holders of other currencies.

"I think that bad news, good action sets the stage for oil, natgas and other commodities in general to just keep rallying," Fisher said.