* April 23 date for reforms could help Saudi MSCI hopes
* Market pulls back as OPEC considers longer output cut
* Lowest trade volume since last September
* Dubai's Union Properties surges after dividend proposal
* Emaar Malls falls after report on Souq.com bid
By Andrew Torchia
DUBAI, March 26 (Reuters) - Middle East stock markets were mixed in mostly thin trade on Sunday, with Saudi Arabia giving up early gains triggered by progress in reforms that could help it to join MSCI's emerging market index.
The Saudi index rose as much as 0.5 percent in early trade but closed 0.1 percent down in its thinnest volume since last September.
The exchange said late on Thursday that it would extend the period for settling trades and introduce short-selling on April 23 in reforms demanded by MSCI. The reforms had been expected in the second quarter, but the date is positive because it gives MSCI time to evaluate their impact before deciding in June whether to put Riyadh on its review list.
However, the market began running out of steam on Sunday after a joint committee of ministers from OPEC and non-OPEC oil producers announced their agreement to review whether a global pact to limit supplies should be extended by six months.
The prospect of an extension suggests that producers are not confident they can succeed in rebalancing the oil market, and Saudi Arabia could end up having to bear much of the burden of output cuts, as it is now. This would limit the government's income and could force it to curb spending.
Much activity focused on smaller stocks, such as Filing and Packing Materials Manufacturing Co, which jumped 3.5 percent in its heaviest trade since August 2014. Arab Bank dropped 3.3 percent as it went ex-dividend.
In Dubai, the index edged up 0.2 percent, with Union Properties climbing by 3.1 percent after its board recommended an 8 percent stock dividend for 2016.
Emaar Malls dropped 0.8 percent after local business magazine Arabian Business quoted sources as saying it was bidding up to $800 million to acquire Souq.com.
This would place Emaar in a bidding war with Amazon.com , which has agreed in principle to buy the online retailer. Emaar Malls did not respond to requests for comment.
Abu Dhabi's index lost 0.7 percent, pulled down by weakness in big banks. Among them was First Gulf Bank with a 1.2 percent decline.
Qatar's index fell by 0.3 percent as petrochemicals blue-chip company Industries Qatar sagged by 2.2 percent.
Egypt's index added 0.6 percent in a broad-based rise, with seven of the most heavily traded stocks gaining and none falling.
* The index edged down 0.1 percent to 6,874 points.
* The index rose 0.2 percent to 3,468 points.
* The index fell 0.7 percent to 4,465 points.
* The index lost 0.3 percent to 10,413 points.
* The index edged down 0.04 percent to 7,041 points.
* The index rose 0.6 percent to 13,108 points.
* The index rose 0.3 percent to 5,654 points.
* The index gained 0.2 percent to 1,379 points.
Editing by David Goodman