Revising up a July forecast of 6.5 percent real GDP growth this year, Samba said record oil prices in late August and a growth in state expenditure in the last three months had contributed to the higher estimates.
The world's biggest oil exporter will record a budget surplus of 208 billion riyals ($55.5 billion), with revenues totalling 551 billion riyals and spending reaching a "moderately stimulative" 343 billion riyals, Samba predicted.
Samba's forecast is based on a $51 per barrel price for Saudi oil - double the $25 a barrel which the bank said the 2005 budget had assumed - and production averaging 9.5 million barrels per day.
"Real GDP for 2005 is set to climb 6.8 percent, the highest growth level achieved in the country for the past two decades," said the report by Samba economist John Sfakianakis.
"Nominal GDP will grow 29.8 percent, a phenomenal rise by any economic standards, and driven by the rise in oil prices."
The bank also revised up its current account surplus forecast to $101 billion from $96 billion.
Saudi Arabia has given no economic forecast but central banker Hamad al-Sayyari told Reuters last week real growth will be "noticeably more" than last year's 5.2 percent.
Sayyari said Saudi Arabia will cut its public debt by as much as the revenues will allow. Samba predicted a fall in debt to 595 billion riyals, or 49 percent of GDP - down from 119 percent just five years ago.
It also forecast central bank foreign assets will rise to $141 billion by the end of the year.
"The Saudi economy is booming and it is at its best performing period ever," Samba said.
But it also said for the first time it had detected signs of price rises and raised its inflation forecast to 1.0 percent this year and 1.6 percent next year.
It said prices may have been increased ahead of the holy month of Ramadan, when demand for many food items increases.
But inflation "will not create any macro-economic distortions," Samba said. "Higher interest rates will also help moderate inflationary pressures." A 15 percent pay rise for state workers ordered by new King Abdullah - the first in 20 years - will add 20 billion riyals to Saudi Arabia's money supply next year and may fuel inflation, especially if matched by the private sector, the bank said.