FDI in petroleum refining activities is restricted when it comes to its participation in Public Sector Undertakings (PSU) carrying out petroleum refining activities. In this case, FDI cannot exceed 49% and cannot imply any disinvestment or dilution of domestic equity in the existing PSU. 
"CHAPTER 3: GENERAL CONDITIONS ON FDI [...]
3.4   ENTRY ROUTES FOR INVESTMENT 3.4.1 Investments can be made by non-residents in the equity shares/fully, compulsorily and mandatorily convertible debentures/fully, compulsorily and mandatorily convertible preference shares of an Indian company, through the Automatic Route or the Government Route. Under the Automatic Route, the non-resident investor or the Indian company does not require any approval from Government of India for the investment. Under the Government Route, prior approval of the Government of India is required. Proposals for foreign investment under Government Route, are considered by respective Administrative Ministry/Department. 
[...]
3.5   CAPS ON INVESTMENTS
3.5.1 Investments can be made by person resident outside India in the capital of a resident entity only to the extent of the percentage of the total capital as specified in the FDI policy. The caps in various sector(s) are detailed in Chapter 5 of this Circular. 
3.6   ENTRY CONDITIONS ON INVESTMENT
3.6.1 Investments by non-residents can be permitted in the capital of a resident entity in certain sectors/activity with entry conditions. Such conditions may include norms for minimum capitalization, lock-in period, etc. The entry conditions in various sectors/activities are detailed in Chapter 5 of this Circular.
[...]
5.2 PERMITTED SECTORS
a) In the following sectors/activities, FDI up to the limit indicated against each sector/activity is allowed, subject to applicable laws/regulations; security and other conditionalities. In sectors/activities not listed below, FDI is permitted up to100% on the automatic route, subject to applicable laws/regulations; security and other conditionalities. [...]
c) Foreign investment in sectors under Government approval route resulting in transfer of ownership and/or control of Indian entities from resident Indian citizens to nonresident entities will be subject to Government approval. Foreign investment in sectors under automatic route but with conditionalities, resulting in transfer of ownership and/or control of Indian entities from resident Indian citizens to non-resident entities, will be subject to compliance of such conditionalities. 
[...]
5.2.4 PETROLEUM & NATURAL GAS 
Sector/Activity | % of Equity/ FDI Cap | Entry Route 
5.2.4.1  Exploration activities of oil and natural gas fields, infrastructure related to marketing of petroleum products and natural gas, marketing of naturalgas and petroleum products, petroleum product pipelines, natural gas/pipelines, LNG Regasification infrastructure, market study and formulation and Petroleum refining in the private sector, subject to the existing sectoral policy and regulatory framework in the oil marketing sector and the policy of the Government on private participation in exploration of oil and the discovered fields of national oil companies.| % of Equity/FDI Cap: 100% | Entry Route: Automatic 
5.2.4.2  Petroleum refining by the Public Sector Undertakings (PSU), without any disinvestment or dilution of domestic equity in the existing PSUs. | % of Equity/FDI Cap: 49% | Entry Route: Automatic [...]" (Government of India/Ministry of Commerce and Industry (2020), Consolidated FDI Policy (Effective from October 15, 2020))
-----------------------------
"The Government of India has reviewed the extant FDI policy on Petroleum & Natural Gas sector and has made the following amendment in the Consolidated FDI Policy Circular of 2020, as amended from time to time (FDI Policy): 2. A new Para 5.2.4.3 is inserted under Para 5.2.4 of the FDI Policy. Accordingly, Para 5.2.4 of FDI Policy is amended to be read asunder: [...]
5.2.4.3 Notwithstanding anything contained at Para 5.2.4.2 above, foreign investment up to 100% under the automatic route is allowed in case an 'in-principle' approval for strategic disinvestment of a PSU has been granted by the Government.[...]" (Government of India/Ministry of Commerce & Industry (2021), Press Note No. 3 (2021 Series))
Government of India/Ministry of Commerce and Industry (2020), Consolidated FDI Policy (Effective from October 15, 2020)
Government of India/Ministry of Commerce & Industry (2021), Press Note No. 3 (2021 Series)
[<a href="https://dpiit.gov.in/sites/default/files/FDI-PolicyCircular-2020-29October2020_0.pdf">Policy</a>],[<a href="https://dpiit.gov.in/sites/default/files/pn3-2021.PDF">PN</a>]