Pennsylvania Gov. Tom Corbett will unveil the final spending plan of his first term in just over a month, yet we already have a pretty good idea of what to expect.

Trouble.

Charles Zogby, the governor's budget secretary, last month warned of a $1.4 billion deficit for 2014-15, and said the upcoming budget could be more difficult than the previous three.

He said he'll consider almost any option to bridge the gap -- the keyword being "almost."

"If there's anything that can help us cover this gap without having to go back to Pennsylvania taxpayers and take more from them in the way of tax increase, then we need to explore that," Zogby said.

Corbett, you'll recall, has pledged not to raise taxes under any circumstance -- even, apparently, if that meant drastically cutting education and social services spending.

And, by the way, that is what it meant during his first three years in office.

It turns out, though, Corbett's pledge is somewhat "¦ elastic.

The governor last year agreed to a $2.3 billion plan to make much needed improvements to Pennsylvania's transportation system. The plan includes gradually lifting the limit on the wholesale tax on gasoline, which has been capped for years.

Corbett tried to make that move conform to his no-tax stance by saying removing a cap isn't the same as raising a levy, but anyone with an ounce of sense knows it has the same effect.

Still, he and some legislators argued, even if wholesale gas sellers have to pay more for their product, that doesn't mean they would pass that on to motorists at the pump.

Nonsense.

Of course they will. The wholesalers flat out said so.

"There will be an immediate impact," said Bob Astor, a spokesman for York-based wholesaler Shipley Energy. "A tax increase of this size can't be absorbed by retail merchants, and they will absolutely pass it on to consumers."

As of Wednesday, wholesalers are now paying an extra dime a gallon, and by 2018 the tax bill paid by wholesalers will increase by 28.5 cents per gallon.

We do not believe hard-working Pennsylvanians should be asked to pay more to close the projected gap, and neither should the Legislature make any more cuts programs benefiting our children, elderly and disabled.

But since the governor has shown some, let's say, wiggle room when it comes to his pledge, there's one tax we think he finally should embrace: A severance tax on the natural gas drillers making a killing in Pennsylvania's Marcellus Shale region.

Corbett has long resisted a severance tax on gas extraction, even though Pennsylvania is the largest natural gas-producing state that does not do so.

The governor opted instead for a paltry "impact fee" in 2012.

It makes no sense to leave this money on the table while cutting programs for Pennsylvanians and, now, taking more from them at the pump.

A bipartisan group of lawmakers agree. Earlier this month they proposed a 4.9 percent severance tax on drillers, which they say would generate $640 million in the first year.

Zogby has been quoted saying he's not aware of any plans by the administration to consider such a tax to close the budget gap.

Corbett, who is running for re-election in 2014, might want to do so.

It might be his last chance.