Previous work with the Nuffield Trust has highlighted that this is a massive challenge in the context of rural trusts. This story tells us.
NHS bosses are increasingly paying premium rates for agency staff to plug holes in rotas, the BBC has found.
Spending in this area rose by 20% last year to hit £3bn in England.
For many shifts, bosses have been so short-staffed they have been willing to breach the government pay caps for these agency workers, most of whom are doctors and nurses.
Separate data supplied by Labour showed some NHS trusts had paid as much as £2,500 to fill shifts.
Out of 60 responses from trusts, 10 reported the most expensive shift cost over £2,000, and for another 13 it was between £1,000-2,000.
The BBC has also seen evidence of aggressive marketing by agencies - which take a cut of the shift pay. One boasted it is the "best" time to try it, because the fees that can be commanded are increasing.
Although paying out £2,500 for one nursing shift may not be the norm - it shows how much supply shortages can cost the NHS.
Saffron Cordery, interim chief executive of NHS Providers which represent trusts in England, said: "Trust leaders consistently raise concerns about sky-high agency costs.
"They're already facing enormous financial pressures with the impact of inflation and energy costs, and the government's failure to fully fund staff pay awards.
"They are doing all they can to minimise agency spend. But safety must always come first."
The government said the NHS faced some exceptional pressures last year, but it expected spending on agency staff to fall in the future.