A manufacture’s representative (sometimes simply called “rep”) is an independent salesperson representing one or several companies. Many manufactures both inside and outside the US use outside sales forces.
From the salesperson’s point you have freedom from company politics and potentially higher income. From the company’s point they only have to pay when something is actually sold.
A typical manufacture’s rep has 8 to 10 clients (or Principals) that have products that don’t directly compete with each other. But the problem in Oil & Gas is there is a shortage of skilled manufacture’s reps, leading to substandard reps entering this market.
If you are interested in learning more, a great place to start is MANA (Manufactures Agents National Association).