Sept 21 (Reuters) - Magellan Midstream Partners' unitholders on Thursday voted in favour of the U.S. pipeline operator's planned sale to larger peer ONEOK Inc for $18.8 billion.

The sale had come under scrutiny with one of the top holders in Magellan, Energy Income Partners LLC, saying in June that it would vote against the deal, due to a burdensom tax structure.

Independent proxy advisory firms Glass Lewis & Co and ISS, meanwhile, recommended a vote in favor of the sale.

According to preliminary results of the meeting, about 96% of the votes cast were in favor of the transaction.

Unitholders, however, voted against compensation to be paid to executive officers related to the deal.

Magellan, in its proxy, cautions that the merger is not conditioned on the compensation vote.

If the acquisition is approved, the executive compensation is payable, Magellan added.

Magellan expects ONEOK to consider the outcome of the vote, along with other factors, when considering future executive compensation. (Reporting by Mrinalika Roy in Bengaluru and Arathy Somasekhar in Houston; editing by Gary McWilliams)