The number of elderly people using free bus passes has dropped on Travel West Midlands services, the company's owner National Express has revealed.
And the parent firm said the collapse of car giant MG Rover was also hitting numbers travelling on some routes in the city.
The news came as National Express yesterday calmed fears over the impact of higher fuel costs on its bus and coach operations today.
The group said its earnings remained in line with expectations despite figures from the AA showing petrol and diesel prices are now at an all-time high.
A spokeswoman for National Express said its Travel West Midlands operation remained a vibrant entity. But she said: "There has been a decrease in the number of our passengers using concessionary fares. We believe there may be may demographic and economic reasons.
"It could be our more mature bus users are more affluent and, perhaps fitter, and hanging on to their cars for longer and using buses less."
She said an update on exact passenger numbers was not being given as part of yesterday's trading statement.
But she did say the collapse of MG Rover - which saw nearly 6,000 jobs axed - has hit the number of people travelling on some routes as they no longer need to get to the Longbridge plant for work, and may have less cash for non-essential journeys.
Innovative measures had been introduced to encourage people to use Travel West Midlands buses, she said. They included a limited stop Aldridge to Birmingham service called Premier Bus to appeal to commuters.
Travel West Midlands spokesman Phil Bateman said the number of users had shot up by 171 per cent since it was introduced in May last year.
The company has also launched a flat 60p rate Bromford Bridge to Birmingham city centre service called Saver Bus.
The idea is to simplify the fare structure - it costs the same for one stop as for travelling the entire route. Cheaper tickets and improvements to its route network were the reasons behind the " sustained growth" in the number of passengers travelling on its coaches during the first six months of this year.
According to the AA Motoring Trust last week, pump prices for unleaded have soared to a record 86.21p a litre, passing the previous record of 86.05p a litre on April 17 this year.
The average cost of diesel had also reached a new high of 90.34p per litre, beating the previous record of 90.17p set on April 11.
National Express doubled its presence in London earlier this month by buying the bus division of Tellings Golden Miller in the capital for £20.4 million. Operating in the Midlands, it owns Central Trains, Silverlink and Midland Mainline, as well as Great Northern, Gatwick Express, Stansted Express, Wessex and One franchises across the country.
It said its trains arm had traded well since the start of January and it was now preparing to submit bids for the Greater Western and the Thameslink and Great Northern franchise in September.
"We continue to work closely with the Strategic Rail Authority and now the Department for Transport on franchise remapping, in particular concerning the future of Central Trains, Midland Mainline and Silverlink," the company added.
National Express shares yesterday closed down 151/2p at 905.5p.