Remarks: UAL 781 treks southwest to LAX from DEN @ FL340 due to some significantly larger company slighty ahead at higher altitudes on the same route. The top most contrail belongs to KL601- PH-BFV from AMS and the contrail at the bottom leading the pack is LH 456- D-ABTH from FRA. These mixed configuration jumbos are maintaining an altitude separation of approximately 1500 feet @FL380/ 365 respectively. All these birds have less than 300 miles to go.