Russia pipeline rules may cut oil exports-trade

* Confusion over new pipeline access law

* Govt may stop firms from selling quotas April 29-source

* Russia exports 5 million barrels per day via pipeline

MOSCOW, April 25 (Reuters) - Russia risks a possible drop in crude oil exports, a key source of the country's budget revenues, due to bureaucratic obstacles over pipeline access, industry sources told Reuters on Monday.

The Energy Ministry sets an export schedule every quarter that fixes volume quotas for each company to ship oil via Russia's oil pipeline network, which is run by state monopoly Transneft. Companies may sell part or all of their quotas on to others.

The sources said, however, that the ministry may bar oil producers from selling on their access to Transneft pipelines following a decree, signed on March 31.

"The registering process for selling the access rights (to Transneft's pipeline) will be halted after April 29," an industry source said.

A spokesman for the Energy Ministry declined immediate comment.

The decree gives top priority for pipeline access to Russian refineries, followed by oil-trading exchanges and domestic suppliers.

Traders said the decree does not clearly define how companies may trade their pipeline access rights. The resulting bureaucratic deadlock may lead to "thousands of tonnes in losses" in export volumes, they said.

Russia delivers abroad around 5 million barrels of oil per day, slightly less than a fifth of total exports from OPEC.

(Reporting by Gleb Gorodyankin; writing by Vladimir Soldatkin; editing by Jessica Bachman and Jane Baird)