Greek stocks outperform Europe with longest winning run since 1991

* STOXX 600 ends up 0.2 pct, euro zone index flat

* Greek stocks rise for 12 straight days

* Well-received updates help Rubis, Ontex, A2A

* Banks mixed: Italy's BPER drops on capital worries

* Dutch lender ING rises after profit beat (Recasts, adds details, closing prices)

By Danilo Masoni

MILAN, May 10 (Reuters) - Greek stocks rose for a 12th straight day on Wednesday, the longest run of gains since 1991, outperforming broadly flat European markets as Athens looked set to clinch vital bailout loans.

While the pan-European STOXX 600 index edged up 0.2 percent and the euro zone STOXX index closed flat, Greek's main equity index rose 1.8 percent.

The gains brought Athens' benchmark index close to erasing all the losses it made after reopening following an emergency five-week bourse closure in the summer of 2015.

The biggest risers were refiner Motor Oil and National Bank of Greece, up 4.8 and 2.4 percent respectively. The increases came as Greek government borrowing costs hit their lowest level in more than five year.

Elsewhere in Europe, some solid earnings updates and gains among commodity-related stocks on the back of rising crude oil prices provided support.

With the European earnings season more than halfway through, financials are among the strongest performers so far, with almost 70 percent of those financial firms which have reported beating expectations, according to Thomson Reuters I/B/E/S data.

Overall, more than 71 percent of European firms have beaten earnings expectations.

Shares in Belgian hygiene products maker Ontex rose 3.6 percent after the firm reported higher revenue in all of its five divisions.

Well-received earnings boosted shares in French energy firm Rubis, which jumped 6.3 percent to hit a record high. A better than expected earnings update at A2A lifted shares in Italy's biggest regional utility up 5.4 percent,

But HeidelbergCement fell 1.2 percent after the cement maker reported its first-quarter operating profit slipped 3 percent as a decline in emerging markets failed to offset a significant rise in Europe and North America.

Banks were mixed with BPER Banca falling 5.7 percent after its first-quarter net profit halved as a result of the writedown of its stake in Italian bank rescue fund Atlante.

"The main share price driver for BPER remains excess capital... and its use. Little has changed on this front with this set of results as there was no news on strategy," analysts at UBS said in a note.

Traders cited worries BPER might may end up buying fellow Italian lender Unipol Banca, hurting its core capital.

ING rose 1.5 percent after its first-quarter underlying pre-tax profit came in ahead of expectations.

Deutsche Bank rose 0.9 percent with a trader citing a Bloomberg report saying Qatar had asked German regulators to allow it to lift its stake in the bank above 10 percent. Two financial sources denied the report. (Reporting by Danilo Masoni and Kit Rees; Editing by Ken Ferris)