Hull Trains has been found to be the worst in the country for paying compensation to customers on time.
The Office of Rail and Road says just over 31% of claims were closed within 20 working days between April and mid-October last year - the national average is 92%.
Hull Trains says it experienced a backlog of claims after two separate periods where services were affected by operational incidents.
A spokesman says: "In two separate periods of 2018, where our services were affected by a number of unrelated operational incidents, we experienced a backlog of claims, causing some processing delays. We apologise for any inconvenience to our customers.
"The situation is improving and we anticipate that we will be back within our customer charter target in the coming weeks - working to the same timeframes that resulted in Hull Trains consistently being ranked amongst the very best train operating companies in the UK."
Stephanie Tobyn, deputy director, consumers at ORR says: "This is the first time ORR has published data on the important area of delay compensation. Passengers have rightly made claims for these journeys and it is good to see that train companies, in the main, are responding to these promptly.
"ORR will be meeting with all train companies later this month to review the current timescales for compensation claims, particularly where these are below target."