WASHINGTON — All six Maryland casinos posted year-over-year gains in gaming revenue in May, for a combined record one-month total of $156.6 million in revenue, breaking the previous record set in March.

That was up 14.7 percent from May of last year.

MGM National Harbor accounted for about 40 percent of gaming revenue generated by all of Maryland’s casinos, a total of $62.3 million, and a 23.2 percent jump from a year earlier.

Live! Casino at Arundel Mills, which opened its $200 million hotel and marked its six-year anniversary last week, had $52 million in gaming revenue in May, up 13.4 percent from a year earlier.

And Baltimore’s Horseshoe Casino posted a gain, with $24.1 million in gaming revenue, up 2 percent from a year earlier.

The state’s three smaller casinos, Hollywood Casino Perryville, Ocean Downs Casino and Rocky Gap Casino Resort, all posted gains as well, led by a 21 percent year-over-year jump at Ocean Downs.

Maryland Lottery and Gaming posts monthly and year-to-date distributions of the state’s share of casino revenue online each month.