The Maryland Senate is expected to weigh a change Friday in the state’s costly practice of acquiring slot machines for privately owned casinos.

The measure was drafted after The Washington Post reported last week that Maryland, one of only a few states where machines are not purchased by casinos, is facing tens of millions of dollars in unanticipated costs.

Sen. Douglas J.J. Peters (D-Prince George’s) said a shift will be considered as an amendment to a larger gambling bill he is sponsoring. On Friday, a Senate committee is expected to vote on that legislation, which would authorize a new casino in Prince George’s County and allow Las-Vegas style table games at all Maryland casinos, contingent on voter approval.

Under the amendment, casino owners would become responsible for procuring and paying for slot machines at their facilities. In exchange, owners would be allowed to keep an additional 8 percent of proceeds.

“It came to our attention through the Washington Post article that this is a provision we should fix,” Peters said.

The gaming floor at Hollywood Casino in Perryville, Md. It's the state's first legalized slots parlor. (Doug Kapustin/FOR THE WASHINGTON POST)

The state is paying an average of about $10,000 per slot machine per year to fill Maryland’s first three casinos, according to a Post analysis. The cost of buying and leasing machines is more than double what officials estimated would be spent per machine in the coming year when lawmakers launched Maryland’s program in 2007.

At the current rate, the state could spend $50 million a year more than projected by the time all five planned casinos are open with nearly 12,000 machines.

Stephen Martino, director of the Maryland State Lottery Agency, said the policy on slot machine procurement was adopted to bring “greater integrity and transparency” to the program. Martino, who arrived in 2010, said that the added precaution probably wasn’t needed. That’s because slot machines in all Maryland casinos are monitored by a central computer system maintained by the state.

Peters’s gambling bill faces tough odds in the remaining weeks of the General Assembly’s 90-day session. Although the bill could pass the full Senate in coming days, House leaders have been lukewarm about supporting another casino.

As written, the Peters bill would seek competitive bids for a sixth site from a swath in western Prince George’s that includes National Harbor, the mixed-use development on the Potomac River, and Rosecroft Raceway, the recently opened horse track in Fort Washington.

Prince George’s County Executive Rushern L. Baker III (D) has said he strongly prefers National Harbor, where he would like to see a billion-dollar casino.

Several religious and citizens groups in Prince George’s are opposed to a casino in the county. On Thursday, a group called Family Faith Future presented what it said were more than 2,000 signatures of Prince George’s voters to House leaders in Annapolis.

“We’re here to remind the legislators of the heart and the voice of the people,” said Bishop Joseph H. Thomas of the Solid Rock Missionary Baptist Church.