The Caterpillar 3516 engine or Caterpillar 3516 generator set is a very popular power source for marine, industrial and petroleum applications.

For oil and gas applications, its quite versatile with petroleum drilling or as well service engines.  They are used as a generator set or to power various pumps or motors, etc.

Here is an example of a petroleum land electric generator set:

There are several companies selling Caterpillar 3516 DITA or similar variations - new or used.

Worldwide Power Products is a company in Houston that offers a variety of Caterpillar 3516B or Caterpillar 3516C engines and generator sets.

One quick search of their inventory online turns up a few options for Caterpillar 3516 diesel generators or engines in stock.