Actually, USCIS is not responsible for allocating immigrant visas. This job is done by the Department of State according to the laws as passed by Congress. USCIS determines if a person or entity is eligible to sponsor a beneficiary when an immigrant visa petition is filed.Approved visa petitions are sent to the Department of Stateu2019s National Visa Center for determination if a visa number is available under the law. If one is, then the petition is sent to an overseas conpost so the beneficiary can apply for a visa or to USCIS if beneficiary is in the US and is eligible to apply for adjustment of status. If a visa number is not immediately available because there are more approved petitions than available visas, the petition is held at NVC until a number is available at which time the petition is transferred as mentioned above. NVC also does some pre-processing such as collecting Form I-864 for beneficiaries who are sponsored, for example.The Department of Stateu2019s monthly Visa Bulletin specifies the number of immigrant visas available each year for each preference category. These numbers are taken from the Immigration and Nationality Act, 8 USC Ch 12 Sub Ch 2 Part 1. Normally visas are issued first come, first served until the annual or per country limit specified in the law is reached. Those petitions affected by the reaching of an annual visa limit must wait until the next fiscal year (October 2023 to September 2023 ix FY 2023. FY 2023 starts on 1 October 2018;) Most petitions are one of two types:: preference category and immediate relative category. Preference category petitions are subject to the numerical limits in the law. Immediate relative petitions are not. Visas issued to immediate relatives however count toward the per country visa limit for the country where the immediate relative was born for the FY in which the visa is issued.