American Missy Franklin can set a record of six golds for the most won at a world championships by a woman in a single edition when she races for favourites the United States in the 4x100 metres medley relay on Sunday.
The last of eight days of racing at the Palau Sant Jordi will also be a chance for Sun Yang of China to match Franklin's compatriot Katie Ledecky in winning a rare treble of distance freestyle titles when the Olympic champion and world record holder goes in the final of the 1,500 metres.
Teenager Franklin won her fifth gold this week in Saturday's 200 metres backstroke, matching the record for golds at a single championships jointly held by fellow American swimmer Tracy Caulkins (1978) and Australian Libby Trickett (2007).
"The competition here is absolutely incredible and they push me in every race I have," Franklin told reporters.
"The 200 back, although it's my favourite, is probably my most painful race," she added.
"It hurt more I think than any other race here has hurt so I'm feeling it a little bit but I'm excited for the relay tomorrow."
There are six more finals on Sunday.
Lithuanian teenager Ruta Meilutyte has another crack at the women's 50 metres breaststroke world record after setting a new best in Saturday's qualifying and Cate Campbell of Australia can win the sprint double in the 50 freestyle after her gold in the 100 on Friday.
Frenchman Camille Lacourt, the 2011 silver medallist, and compatriot Jeremy Stravius were quickest in the 50 backstroke semi-finals and Kosuke Hagino of Japan is among the favourites in the men's 400 metres individual medley.
The final event of the championships sees Franklin competing in the 4x100 medley, immediately after the men's version.