More carriages are being added to the sleeper train from Cornwall and Devon to London.
First Great Western said the move was necessary because of an increase in the demand for the "Night Riviera" service from Penzance to Paddington.
The company believes this is because people are trying to save money on London hotel costs.
Regional general manager, Julian Crow, said First Great Western is considering expanding the service further.
"We're watching carefully how business develops," he told BBC News.
The sleeper carriages can now accommodate 60 passengers during the week and 75 at the weekend.
The weekday train leaves Penzance at about 2130, arriving at London Paddington at about 0530 the following morning.
Thousands of people signed a petition when the service came under threat in 2005.
It was running at a loss and had to rely on a £5m annual subsidy from the Department of Transport, but when First Group was awarded the new franchise from April 2006, it said the service would be retained and extended.
"This is a very good step forward," Mr Crow said.