The Calabasas staffing company On Assignment Inc. has moved to acquire Massachusetts-based Oxford Global Resources for $200 million. On Assignment will pay $190 million in cash and $10 million in common stock for the company, which provides engineering and tech staffing services. Oxford shareholders will also have the chance to receive an earn-out of up to $12 million based on the company’s performance over the next two years. Oxford is expected to report 2006 revenues of $177 million, a 20 percent increase from 2005. Gross margins over the last three years have been in excess of 34 percent, On Assignment said.