Divers Ltd., AMF Yacht Charters, Ocean Quest Cruise Lines, G2 Publishing (Fathoms Magazine), Sea Ventures Ltd., and Uwatec.

[citation needed] Gilliam formed the consulting service Ocean Tech in 1971 and provided expert witness testimony for diving and maritime related legal cases.

He also was sponsored as a surfing competitor for Hobie and Hansen surfboards[citation needed] and participated in contest events on the east and west coasts (and Caribbean) as well as promotional sales activities for those manufacturers from 1965 to 1970.

[5] He won a National ROTC Scholarship in 1968 and was scheduled to be commissioned as an Army officer when he was recruited to do alternate service on a Navy deep diving project filming nuclear fast attack submarines.

[citation needed] Gilliam left his undergraduate studies early to join the Navy project and then went on to pursue a business career by starting Ocean Tech.

[4] In 1972 off the island of St. Croix, Gilliam's dive buddy Rod Temple was attacked by oceanic whitetip sharks during a project and was killed.

Gilliam was cited for heroism by the Virgin Islands' Governor for his attempt to save Temple when he broke off his decompression and swam back into the attack.

[6] The company (and others that followed) also had a filming and studio support division that provided location services for boats, diving, equipment, helicopter & aircraft, stunt persons, and local logistics for Hollywood movies, television series, documentaries, and tourism promotions.

Film work included movies such as "Pleasure Island", "The Deep", "The Island of Dr. Moreau", "The Man Without A Face", "Dreams of Gold", "Going Overboard", "The Island", "Having A Ball", "Abyss", "The Dive", "Message In A Bottle", "Head Above Water", as well as television productions such as "Miami Vice", "Greatest American Hero", "ABC Sports", "Undersea World of Jacques Cousteau", "HBO", "Showtime", "Discovery Channel", "National Geographic Explorer", "Travel Channel", "Cinemax", "Today", "NBC's live broadcasts of the 1983 America's Cup Races", "Encore Productions", "BBC", and "The Playboy Channel".

Gilliam also began conducting research on dive computer safety during this time[9] and remained with Ocean Quest until the company was sold to Sea Escape Cruise Lines in the fall of 1990.

In 1991, Gilliam joined Dick Rutkowski, Tom Mount and Billy Deans on the board of directors for International Association of Nitrox and Technical Divers (IANTD).

[13][14] Gilliam remained President and chief executive officer of International Training Inc until February 5, 2004, when it was sold to investors backing Brian Carney who had been serving as the General Manager.

[16] Gilliam was instrumental in assisting UWATEC's founder and owner, Heinz Ruchti, with the sale of the company to Johnson Outdoors the following year for nearly $50 million.

[16] Gilliam stepped down in November 1998 when Johnson Outdoors merged UWATEC USA with ScubaPro and relocated the company to El Cajon, California.