* Saudi's PetroRabigh plunges 10 percent daily limit
* Bupa Arabia climbs; parent to boost stake at high price
* Dubai's Amlak, DXB Entertainments slide in wake of earnings
* Oman moves little after debt downgraded to junk
* IMF agreement may mean tighter monetary policy for Egypt
By Andrew Torchia
DUBAI, May 14 (Reuters) - Most Gulf stock markets edged down on Sunday with Saudi Arabia dampened by a much wider first-quarter loss at PetroRabigh, while agreement between the International Monetary Fund and Cairo did little to help Egypt's bourse.
The Saudi stock index slipped 0.4 percent as PetroRabigh tumbled its 10 percent daily limit after reporting that its quarterly loss ballooned to 240 million riyals ($64 million) from 37 million riyals a year earlier, and compared to a profit in the previous quarter.
The company blamed the bigger loss, which contrasted with solid first-quarter earnings at many Saudi petrochemical firms, on reduced margins for refined products and a downtrend in crude oil prices, which hit inventory valuations. Also, the firm reclassified some payments and temporarily shut a facility in the first quarter.
The stock had been in a strong uptrend since mid-March in anticipation of good first-quarter earnings.
Medical insurer Bupa Arabia climbed 4 percent to 116.50 riyals after saying its international parent Bupa would increase its stake to 34.25 percent from 26.25 percent, by purchasing part of Nazer Group's stake. The planned purchase would occur at a price of 143 riyals per share.
But another insurer, MedGulf, plunged 10 percent after saying it had swung to a 93 million riyal loss in the quarter from a year-earlier profit. It cited a jump in provisions for doubtful debts and lower net underwriting income.
Dubai's index edged down 0.1 percent in thin trade as Islamic real estate finance firm Amlak dropped 2.9 percent after reporting net profit of 7.5 million dirhams ($2.0 million) for the first quarter. A year ago, it had reported profit attributable to equity holders of 122.1 million dirhams.
Amusement park operator DXB Entertainments sank 3.3 percent to its lowest level since August 2015. Last Wednesday, it reported a 291.8 million dirham loss for the first quarter and said attendance at its parks, which has disappointed investors, was likely to dip in the coming two quarters.
Qatar's index slipped 0.5 percent, partly because of a 1.3 percent pull-back by Qatar National Bank. But the most heavily traded stock, Vodafone Qatar, surged 2.6 percent.
The Omani market edged down 0.2 percent after Standard & Poor's cut Oman's credit rating to junk status, saying low oil prices had eroded the country's external reserves to the point they could no longer offset the threat of low oil prices.
Trade was very thin. Analysts had expected banking stocks to be most vulnerable to the downgrade because it could mean the banks face higher costs in financing themselves, but while Bank Muscat and Bank Sohar fell modestly early on Sunday, National Bank of Oman rose.
In Egypt, the IMF said on Friday it had reached a staff-level agreement with Cairo on a second loan instalment, and would make available about $1.25 billion.
The agreement had been expected, but it came sooner than some analysts had anticipated, and was accompanied by an IMF statement that the finance ministry had drafted a "very strong budget" which, if enacted by parliament, would put public debt on a "clearly declining path to sustainable levels".
However, the Egyptian stock index fell 0.3 percent. In its talks with Cairo, the IMF stressed the need to bring down inflation, which could mean tighter-than-expected monetary and fiscal policy in coming months.
Global Telecom dropped 4.3 percent, continuing a slide that began on Thursday when it reported a first-quarter net loss attributable to shareholders $26 million versus a profit of $48 million a year ago.
Naeem brokerage said it was reviewing its recommendation for Global, blaming the loss on weakness at the company's Algerian business and rising overheads.
* The index fell 0.4 percent to 6,853 points.
* The index edged down 0.1 percent to 3,416 points.
* The index dropped 0.3 percent to 4,593 points.
* The index lost 0.5 percent to 10,062 points.
* The index slid 0.3 percent to 12,871 points.
* The index fell 0.2 percent to 6,659 points.
* The index rose 0.3 percent to 1,310 points.
* The index dropped 0.2 percent to 5,420 points.
Editing by Andrew Torchia/Keith Weir