The Welsh Government would aim to scrap air passenger duty (APD) on long-haul flights if the tax was devolved, First Minister Carwyn Jones has said.
Costing around £1m a year, a report for Welsh ministers by aviation consultants estimates it could boost annual Cardiff Airport passenger numbers by 62,000.
The new research described the effect on Bristol Airport as "marginal".
UK ministers said they ruled out devolving APD after considering the impact on English airports nearby.
Consultants Northpoint's research also suggests abolishing the tax on all flights, combined with additional route development incentives, could raise Cardiff passenger numbers by nearly 50%, adding 658,000 extra passengers a year by 2025.
On economy class outbound flights of over 2,000 miles, passengers currently pay £75 in tax, rising to £78 next April.
The duty on long-haul business class journeys is £150, increasing to £156 in 2018.
Mr Jones said: "Why is it that Scotland has been given that power and Wales hasn't got that power?
"We could really grow Cardiff Airport, we could help to grow other airports across Wales, if air passenger duty was devolved, and we know it doesn't come at anyone else's expense.
"This is not about taking passengers from other airports, those that are over the border, this is about growing demand in Wales."
Asked by BBC Wales if he would scrap APD if he had the power, he said: "That's where we'd start, it would cost around £1m [a year], and our budget is £16bn, more or less.
"It's a small amount of money, but the economic boost would be far more than £1m, but yes we start from the position of looking to get rid of it, certainly not to increase it."
The Welsh Government bought Cardiff Airport, near Rhoose in the Vale of Glamorgan, for £52m in 2013, after a slump in passenger numbers.
In April, Qatar Airways announced it would introduce flights from Cardiff to the Middle East.
It is adding daily flights to Doha, Qatar's capital, from May 2018. Once it starts, the service will be the only scheduled long haul route from the airport.
Attracting long-haul destinations has been part of the airport's strategy for growth.
Meanwhile, on the shorter trip front, Flybe has just announced plans to start direct flights from Cardiff to Venice in Italy from summer 2018.
They plan to run flights twice a week from Wales from March to September.
A UK government spokesperson said it had "looked at the issue of APD devolution in detail over recent years in line with our commitment in the St David's Day Agreement [on Welsh devolution].
"We made our position clear on this matter last year. Having considered the impacts of devolving APD on nearby English regional airports, we have ruled out the devolution of APD to Wales."
Lots of readers responded to Carwyn Jones's air passenger duty comments on the BBC Wales News Facebook site.
Lesley Jamie Sinclair said: "We would use Cardiff airport more if they would fly more flights to the US."
Janet Jones commented: "On our way to Bristol Airport now-the same holiday from Cardiff was a lot more expensive and we only live 20 mins away."
Ann Smith added: "I definitely would use Cardiff, be good if better public transport to and from though.
"I use EasyJet from Bristol but would prefer to fly from Cardiff any day."