Marshall has held Permian and Delaware Basin Drilling Supervision and Drilling Engineering leadership positions for the past 15 years and Mud Engineering positions for the last 30 years. His competence is such that he can work totally independent of supervision, as a team leader or as a team member.

Though his positions have been primarily in drilling and mud engineering, he makes a point to be involved with the well planning, AFE costing and site preparation leading up to drilling, cost accounting, vendor evaluations and selections, completions and surface facilities and operations supervision.

Since he has much mud engineering expertise, he serves as mud engineer for wells on which he is the drilling supervisor. He also served as Operations Manager for Probity Energy responsible for all aspects of the drilling, facilities and production functions. His safety record is impeccable.