Infamously, the SNP's envisioned post-independence budget was based on their forecast for annual oil and gas revenues: £10bn. In reality they have averaged an order of magnitude less: £1bn.
Oil and gas are volatile commodities so there will be year-to-year fluctuations but the secular trend is clearly downwards. The best wells have run dry, and the UK is committed to net zero by 2050 and Scotland to net zero by 2045.
[1] https://www.economicsobservatory.com/what-might-the-public-f...