The number of rigs drilling for oil in the U.S. climbed seven in the past week to 425, continuing a trend of increases, according to oil-field services company Baker Hughes Inc. BHI 0.52 % The U.S. oil-rig count is typically viewed as a proxy for activity in the sector. After peaking at 1,609 in October 2014, low oil prices put downward pressure on production and the rig count fell sharply. The oil rig count has generally been rising since the beginning of the summer, as many oil producers believe drilling in some U.S. regions can be profitable even with oil prices in their recent range of $40 to $50 a barrel. The nation’s gas-rig count rose by four to 96 in the past week. The U.S. offshore-rig count rose to 22, up from 20 last week.