The C.D. Howe Institute says that's because of resource revenue volatility.
Colin Busby, co-author of the report, says Saskatchewan is at the bottom of the pack for spending overruns because if resource revenue is higher than the budget is predicted, there is no set plan as to where that money will go.
Instead of going into new programs, Busby says it should go to pay down the deficit or to lowering taxes.
Busby says it's not a matter of balancing the budget by looking at a surplus or deficit because that often overshadows what's happening to revenues and spending, and the government's plans for both.
The report says federal, provincial and territorial governments have a cumulative spending overrun of more than $53 billion over the past ten years.
Saskatchewan's share of that is $4.2 billion.