All five were pronounced dead ar the scene, reports CBS station KTVT-TV.
Fort Worth Police Lt. Ric Clark said the driver of the second truck was airlifted to Harris Methodist Hospital in Fort Worth, where he was reported to be in serious condition.
"He probably never even saw them, until he was literally on top of them," Clark said.
The crash happened about 1 p.m. Sunday as the truck, which witnesses said was traveling at excessive speeds, was merging onto Interstate 30 on the west side of Fort Worth, Clark reported.
"It crossed the median and then started flipping in the air, side over side," Clark said. "It crashed into a green Chevy truck going east on I-30 in the right-hand lane. Both vehicles were completely totaled. It was massive damage."
That section of the highway was closed for five hours.
The driver, Edward Jennings, 18, was thrown between 70 and 80 feet from the vehicle.
The Tarrant County Medical Examiner's Office identified the other four victims as Hank Gorman, 20; John McDonald, 16; James McDonald, 15; and Martin McDonald, whose age is unknown.
Police said they didn't know how the McDonalds were related to each other, but said all five lived in the Fort Worth area.