Troubled East Midlands Ambulance Service (EMAS) is struggling financially and has some of the worst response times in England.
It is thought the trust’s non-executive directors want to merge with West Midlands Ambulance Service.
Both trusts said discussions on a “range of options” had taken place but talks were at an early stage.
If the merger goes ahead, the new service would cover a population of 10.4m people and cover 11,500 sq miles.
EMAS recently applied for a loan after ending the year £12m in debt, and chief executive Sue Noyes stood down last month. Its response times to the highest-priority emergency calls in 2014-15 were well below national targets.
It is understood EMAS first approached the West Midlands trust – which had some of the best response times in the country – for help around six weeks ago.
The BBC understands that although the non-executive directors at EMAS believe a merger is the right option, there is resistance from the trust’s other management.
In a letter to staff, chairwoman Pauline Tagg said she had been talking to WMAS about the potential for chief executive Dr Anthony Marsh, to provide support.
“This option, and others, is still being explored and discussions have not yet come to a conclusion,” she said.
It is understood Mr Marsh, who previously took on a part-time role as head of the East of England Ambulance Service, was interviewed by EMAS.
However, sources told the BBC Dr Marsh, who was heavily criticised over his salary in the dual roles, was concerned he would face similar attacks if he stepped in to oversee the East Midlands Trust.
In a statement, West Midlands Ambulance Service confirmed it had been approached “to explore how we might assist” and “a range of options” had been discussed but nothing yet agreed.
Dr Anthony Marsh is the chief executive of West Midlands Ambulance Service
Dr Iestyn Williams, senior lecturer in health policy and management at the Health Services Management Centre in Birmingham, said that large mergers are complex and often do not provide the anticipated benefits.
“It can cost millions of pounds and run into years.
“The productivity and efficiency can be affected and it can be years before the benefits materialise.”
How the services compare:
West Midlands Ambulance Service
Serves population of 5.6m
Area: More than 5,000 sq miles covering Shropshire, Herefordshire, Worcestershire, Staffordshire, Warwickshire, Coventry, Birmingham and Black Country
Number of calls a day: 3,000
Number of staff: 4,000
East Midlands Ambulance Service
Serves population of: 4.8m
Area: 6,425 square miles covering Derbyshire, Leicestershire and Rutland, Lincolnshire, Northamptonshire and Nottinghamshire
Number of calls a day: 2,000
Number of staff: 2,700