RIDGEWOOD ENERGY Y FUND LLC

The Fund had no drilling activity for exploratory wells during the years ended December 31, 2025 and 2024. The following table sets forth the Fund’s developmental well drilling activity during the years ended December 31, 2025 and 2024. Gross well is the total number of well in which the Fund has a working interest. Net well is the sum of the Fund’s fractional working interests owned in the gross well. The Marmalard Well #5, which produces both oil and natural gas, is located in the offshore waters of the Gulf of America and was completed during the year ended December 31, 2024. Due to a downhole mechanical failure, the well needed a sidetrack operation performed in order to resume production which was completed during the year ended December 31, 2025.

Gross · Net · Gross · Net

Development wells:

Productive · 1 · 0.01 · 1 · 0.01

In-progress · - · - · - · -

Development well total · 1 · 0.01 · 1 · 0.01

Unaudited Oil and Gas Reserve Quantities

The preparation of the Fund’s oil and gas reserve estimates are completed in accordance with the Fund’s internal control procedures over reserve estimation. Such control procedures include: 1) verification of input data that is provided to an independent petroleum engineering firm; 2) engagement of well-qualified and independent reservoir engineers for preparation of reserve reports annually in accordance with SEC reserve estimation guidelines; and 3) a review of the reserve estimates by a third-party independent petroleum engineering firm.

The Manager’s primary technical person in charge of overseeing the Fund’s reserve estimates has a B.S. degree in Petroleum Engineering, a Master of Business Administration, and is a member of the Society of Petroleum Engineers, the Association of American Drilling Engineers and the American Petroleum Institute. With over thirty-five years of industry experience, he is currently responsible for reserve reporting, engineering and economic evaluation of exploration and development opportunities, and the oversight of drilling and production operations.

The Fund’s reserve estimates as of December 31, 2025 and 2024 were prepared by Netherland, Sewell & Associates, Inc. (“NSAI”), an independent petroleum engineering firm. The information regarding the qualifications of the petroleum engineer is included within the report from NSAI, which is filed as Exhibit 99.1 to this Annual Report, and is incorporated herein by reference.

Proved Reserves. Proved oil and gas reserves are estimated quantities of oil and natural gas, which geological and engineering data demonstrate with reasonable certainty to be recoverable in future years from known reservoirs under existing economic and operating conditions. Proved developed oil and gas reserves are proved reserves expected to be recovered through existing wells with existing equipment and operating methods. Proved undeveloped oil and gas reserves are proved reserves expected to be recovered through new wells on undrilled acreage, or through existing wells where a relatively major expenditure is required for recompletion. The information regarding the Fund’s proved reserves, which is contained in Item 7. “Management’s Discussion and Analysis of Financial Condition and Results of Operations” of this Annual Report under the heading “Critical Accounting Estimates – Proved Reserves,” is incorporated herein by reference. The information regarding the Fund’s unaudited net quantities of proved developed and undeveloped reserves, which is contained in Table III in the “Supplementary Financial Information – Information about Oil and Gas Producing Activities – Unaudited” included in Item 8. “Financial Statements and Supplementary Data” of this Annual Report, is incorporated herein by reference.

Proved Undeveloped Reserves. As of December 31, 2025, the Fund had proved undeveloped reserves related to the Beta and Marmalard projects totaling 0.1 million barrels of oil, 9 thousand barrels of natural gas liquid (“NGL”) and 0.1 million mcf of natural gas. As of December 31, 2024, the Fund had proved undeveloped reserves related to the Beta and Marmalard projects totaling 0.1 million barrels of oil, 14 thousand barrels of NGL and 0.1 million mcf of natural gas. The Beta and Marmalard projects were determined to be discoveries in 2012. The Beta Project commenced production in 2016 and the Marmalard Project commenced production in 2015.

The decrease in total proved undeveloped reserves at December 31, 2025 was primarily due to the conversion of one Marmalard well’s proved undeveloped reserves to proved developed producing reserves related to a sidetrack operation completed during the year ended December 31, 2025.

The proved undeveloped reserves relating to the Beta Project, which were initially assigned at the end of the year 2021 and 2022, are associated with planned well recompletions. The Fund did not incur costs during the year ended December 31, 2025 to advance the development of its proved undeveloped reserves related to the Beta Project. The Fund expects additional recompletion operations to be completed in 2026 related to the Beta Project.