Oil markets climbed for a sixth day on Tuesday, boosted by a tighter supply and firm demand outlook, but power shortages in China which hit factory output tempered the rally. Brent crude had gained 12 cents, or 0.1%, to $79.65 a barrel at 1358 GMT, after reaching their highest level since October 2018 at $80.75. Brent gained 1.8% on Monday.