Russia's Transneft, the operator of the world's largest oil pipeline network, has taken the unprecedented step of imposing caps on oil received by it as storage filled up amid weak Western demand for Russian oil, Reuters reports citing five sources familiar with the matter.

While Russian oil exports are still flowing - especially in the direction of India and China - despite self-imposed sanctions by western energy buyers, difficulties with payments, insurance and shipping as well as curbs on dealing with several Russian oil suppliers forced many regular buyers to shun the market, leaving barrels unsold.

And as the oil plumbing has literally clogged up, Transneft has told several Russian oil firms it would limit intake to its system amid high volumes of stored oil, which affect flexibility and threaten normal operations.

Transneft's curbs cover oil that has yet to find buyers, while companies that have no difficulty selling cargoes would be allowed to supply all their oil to the system, two Reuters sources said.

As reported previously, more than a dozen cargoes of Urals oil from the March loading plan were cancelled, postponed or replaced amid weak demand, traders said, while Russian firms had to divert extra volumes for export, as domestic refinery runs declined. Furthermore, Russian oil giants Surgutneftegaz and Zarubezhneft did not award spot tenders this month.

That said, Russia's pipeline capping may reverse soon: while the Urals oil loading plan for April has been increased significantly, May is looking stellar with Bloomberg reporting that according to the loading program, a total of 33 cargoes of Russian ESPO crude totaling 3.3m tons (all cargoes in May program are 100k tons) are scheduled to be shipped from the port of Kozmino in May. This equates to 780k b/d, a record, compared with 3.1m tons or 757k b/d in April.

Last week, Russia indicated that it aims to ship the largest amount of its flagship Urals crude in almost three years in April.