CAIRO, Dec 30 (Reuters) - Oman"s budget deficit reached an estimated 1.2 billion rials ($3.12 billion) in 2021, or 3.8% of gross domestic product, the Gulf country"s finance ministry said on Thursday. Nominal GDP growth was estimated at 13.8% for 2021, the ministry added. The figures mark a sharp rebound from Oman"s yawning deficit of 19.3% of GDP in 2020 caused by battered oil prices and the pandemic"s impact. One of the weakest economies in the oil-rich Gulf, Oman last year launched a medium-term fiscal plan to fix its heavily-indebted finances. Oman said it expected its debt-to-GDP ratio to come in at 68% this year, which it said was below its own projection of 83%. Foreign reserves at the central bank are estimated at $18 billion in 2021 from $14 billion in 2020. Earlier this month, Oman projected a budget deficit of 5% of GDP in 2022. Total spending is expected at 12.1 billion riyals next year. read more Fitch revised its outlook on Oman earlier this month to "stable" from "negative", as higher oil prices and fiscal reforms helped improve the sultanate"s balance sheet. read more ($1 = 0.3847 Omani rials)