A few days into the experiment, the new world of legal-recreational-marijuana sales in Colorado appears to be a big success — so much so that pot shops are finding it impossible to keep up with demand.

According to the Denver Post, at least 37 stores in Colorado were licensed to sell recreational pot to anyone 21 or over as of New Year’s Day. The Associated Press and others reported long lines outside Denver pot shops, with some eager customers forced to wait three to five hours before getting a chance to go inside, step up to the counter and make a purchase.

Prices have been steep — in some cases, stores were charging $50 or even $70 for one-eighth of an ounce of pot that cost medical marijuana users just $25 the day before — and taxes add on an extra 20% or so. Even so, sales have been brisk.

The two operational pot shops in Pueblo collectively sold $87,000 of marijuana on Jan. 1, per the Pueblo Chieftain, and store owners say if demand persists anywhere near the current high, they’ll be sold out in the very near future. Likewise, Toni Fox, owner of the 3D Cannabis Center in Denver, told the Colorado Springs Gazette that a sellout is imminent. “We are going to run out,” she said on Thursday, Day 2 of legal-recreational-marijuana sales. “It’s insane. This weekend will be just as crazy. If there is a mad rush, we’ll be out by Monday.”

Another Associated Press story noted that some shops had to close early on Wednesday because they didn’t have enough marijuana on hand to oblige customers.

(MORE: Colorado’s ‘High Country’ Takes On New Meaning)

For more than a month, many have speculated that Colorado pot shops would not be able to meet demand due to the limited number of stores open in the state, as well as tough regulations regarding how marijuana is grown and distributed at the wholesale level. Of course, strong demand — especially from “smoke birds,” a.k.a. out-of-state tourists visiting Colorado for legal marijuana purchases — also plays a big role. By most accounts, since Jan. 1 more than half of pot sales have gone to non-Coloradans.

Prices in legal pot shops have already risen to upwards of $400 an ounce. Once you factor in taxes, as well as the fact that it looks like shops may periodically be sold out for a while, and some are saying the situation is one that could push pot enthusiasts back to buying marijuana on the black market. “People will get real tired of paying the taxes real fast,” one street dealer in Pueblo named Tracy told the Chieftain. “When you can buy an ounce from me for $225 to $300, the state adds as much as $90 just for the tax.”