"Having two separate receptions is quite redundant, and considering that most of the guests overlap it makes more sense to co-host the party," said one source with direct knowledge of the matter who declined to be named.

Aramco became the single largest shareholder of S-Oil in January 2015, part of its drive to expand its footprint in the downstream petroleum sector and establish commercial offices in global oil trading hubs like Singapore.

Aramco did not respond to a request for comment.

An S-Oil spokesman confirmed the joint reception and said the South Korean refiner has co-hosted receptions with many other companies at events for global clients.

Last year, S-Oil and Aramco hosted separate APPEC events. This year's joint reception will be held at the Ritz Carlton hotel on Sept. 25, the second day of the conference.

Aramco traditionally sells most its crude oil under long-term deals with fixed monthly volumes and prices, but the company is in a drive to become more commercially minded, and plans to gradually increase the amount of cr
ude and refined products it freely trades. (Link: https://reut.rs/2PxeyoQ

Aramco's trading office in Singapore, which opened in 2015 but only stepped up hiring in 2017, is its first overseas trading operation. The Singapore office handles physical and derivatives oil trading for its joint venture operations in Asia, which include the partnership with S-Oil and another with Japan's Showa Shell, said a second source.

S-Oil is South Korea's third-biggest refiner, selling fuels like gasoline, diesel or jet fuel globally. Its main supplier of feedstock crude oil is Saudi Aramco.

Singapore's APPEC, which this year takes place from Sept. 24-26, is one of Asia's biggest annual petroleum industry gatherings, during which producers, refiners and merchants sign and renew supply deals and exchange information.

In one such event, APPEC will also host a reception by French oil major Total, Nigerian National Petroleum Corp and their project partners to launch Egina crude, according to a copy of an invitation seen by Reuters.

The Egina field in Nigeria is expected to start production in December.

(Reporting by Jessica Jaganathan; additional reporting by Jane Chung in SEOUL; Editing by Henning Gloystein and Tom Hogue)

By Jessica Jaganathan