By Eyk Henning

FRANKFURT--Renova, a holding company of Russian oligarch Victor Vekselberg, on Friday said it has bought a 4.99% stake in U.S. oil-industry equipment firm Dresser-Rand Group Inc (DRC).

The announcement adds a twist to speculation on the future of Dresser-Rand. Mr. Vekselberg's Renova also holds a 33.19% stake in Swiss pump maker Sulzer AG (SULZF), which earlier said this week it was in non-exclusive talks with the U.S. company about a potential transaction.

At the same time, German conglomerate Siemens AG (SIEGY)is preparing a multi billion-dollar offer for Dresser-Rand, people familiar with the matter said on Friday.

A Siemens offer of more than $6 billion, or more than $80 dollar per share, could be more attractive to Dresser-Rand than an offer from Sulzer, the people said.

Siemens declined to comment.

Write to Eyk Henning at eyk.henning@wsj.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires