Global oil prices have tumbled almost 60 percent since June, hitting five-year lows as growing production and tepid global demand has caused a supply glut and prompted oil producers to scale back spending. “We expect our headcount adjustments to be in line with our primary competitors,” Halliburton’s Chief Operating Officer Jeffrey Miller said on a post-earnings call on Tuesday, without giving a specific number. Baker Hughes, which is being acquired by Halliburton in a near-$35 billion deal, said earlier in the day it would lay off 7,000 employees.