Hospital bosses shelled out more than £12m in the past two years on 251 locum doctors and consultants.
Figures revealed under Freedom of Information laws show that in 2012/13 Lancashire Teaching Hospitals Trust spent £5.8m with locum agencies to temporarily fill posts.
And in 2013/14 the Trust, which runs the Royal Preston Hospital and Chorley and South Ribble Hospital, spent £6.8m.
In 2012/13 they used 153 locum doctors and in 2013/14 they used 198 at a cost of £12,746,430 - averaging almost £51,000 per post.
Today the Trust said an increase in the use of locum doctors is due to a number of issues including an increase in vacancies due to a national shortage of doctors in certain specialist areas.
The figures, which were released through the What Do They Know website, show that areas where more locum doctors were used include general medicine, general surgery, paediatrics and neonatal, obstetrics and gynaecology and plastic surgery.
In 2012/13 the Trust used 61 general medicine locums, this increased to 76 in 2013/14,
There was also a year on year increase in the number of locums used in paediatrics and neonatal. In 2012/13 the figure stood at 19, which increased to 26 in 2013/14.
In it’s response to the FOR request the Trust said it struggled to recruit staff in consultant radiology and haematology, middle grade A&E, general medicine and paediatrics roles.
Karen Swindley, workforce and education director at Lancashire Teaching Hospitals NHS Foundation Trust said: “Wherever possible we always try to use our own staff rather than locums.
“However, there is a national shortage of doctors in some specialist areas and our priority is always the safety and care of our patients.
“Therefore, if required, we will use locums to ensure that we maintain high standards of care for our patients.
“We have seen an increase in the number of locum doctors for a number of reasons, including an increase in vacancies due to a national shortage, an increase in demand for healthcare and investment in improved ways of working to ensure patients receive timely care.”
Karen added: “We are continuously reviewing our staffing levels and have a recruitment strategy in place to ensure that we have the appropriate number of people in the right posts.”
The hospital trust uses a company called Medac to fill the posts.