Serena and Venus Williams have been taking in the sights in Doha
Serena Williams will take on elder sister Venus in the group stages of the season-ending Tour Championships in Doha, which begin on Tuesday.
The Americans have been drawn in the Maroon Group, along with Russians Elena Dementieva and Dinara Safina.
Serbians Jelena Jankovic and Ana Ivanovic, and Russians Svetlana Kuznetsova and Vera Zvonareva, make up the White Group.
Two players from each group will advance to the semi-finals.
Kuznetsova will take on Zvonareva in the opening match at 1400 GMT on Tuesday, followed by Jankovic against Ivanovic, and Safina against Venus WIlliams.
The tournament, which takes place in Doha for the first time, is without its defending champion following the retirement of Justine Henin in May.
Australian Open champion Maria Sharapova is also absent because of a shoulder injury.
Serena Williams claimed the world number one ranking after winning the US Open in September, but Jankovic has since regained the position and will end the year at the top of the rankings no matter what the result in Doha.