Engineering Services

Our services are extensive, ranging from SEC and PRMS reserves evaluations, economic forecasting, analytical modeling, fair market values, integrated field studies, reservoir engineering, site inspection, geology, geophysics, petrophysical analysis, resource forecasting, restructuring and operating support, ESG advice, GHG Reporting, domain expertise for AI and machine learning to litigation support.

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H.J. Gruy and Associates, Inc. is a registered engineering firm with the Texas Board of Professional Engineers. H.J. Gruy and Associates, Inc. will rertain the services of a properly registered firm to perform any work which involves the non-exempt public practice of geoscience in Texas or elsewhere.

70 Years of Experience Serving the Energy Industry

Our clients include major integrated energy companies, independent oil and gas producers, government agencies, banks, private equity firms, venture capitalists, and attorney groups. Our annual reserve reports, performed for our client's public filings, are accepted by the U.S. Securities and Exchange Commission, and our economic projections for asset evaluation are accepted by financial intitutions worldwide. We have completed contracts for the U.S. Government, and our security clearances are current.


H.J. Gruy and Associates, Inc. provides a wide variety of professional services ranging from independent reserves reports to forensic enginering, litigation support, fair market value, site inspection, ESG and GHG reporting, and more.

Contact us for an overview of our most recent completed projects.

Discover Our Recently Expanded GHG Reporting Services

Open Our GHG Bulletin

ESG and GHG Services

Greenhouse Gas (GHG) Emissions Disclosures - Gruy personnel have the expertise to provide Scope 1, 2, and 3 GHG emissions reports or audits conforming to various frameworks, applying robust standards, and summarizing complex scenarios with meaningful charts and graphs. With an excellent reputation, we generate credible deliverables that comply with policies published by governmental agencies.

Environmental, Social, and Governance - Our organization, with 75 years of experience, provides products that are recognized and accepted as accurate and objective. Gruy can assist with analyzing critical ESG criteria and metrics, helping to boost long-term sustainability and increase efficiencies.

Independent Reserves Reports

We regularly provide the engineering and economic forecasts required by the U.S. Securities and Exchange Commission for value reporting. H.J. Gruy and Associates, Inc. has a long-standing reputation for producing respected reserve estimates and economic projections, with accompanying reports, that conform to the guidelines published by the S.E.C. and the Financial Accounting Standards Board.

Our professionals have a wealth of experience forecasting production from conventional reservoirs and resource plays using modern decline curve analysis techniques.

Restructuring & Operations Support

We provide technical engineering support for corporate financial restructuring and bankruptcy proceedings. In these situations, Gruy has a proven record of positive outcomes for our clients. Furthermore, we have the capabilities to provide interim oil field operations with uninterrupted regulatory compliance, hazard assessment, and comprehensive site inspection for assets in transition.

Probabalistic Reserve Estimates

Our engineers and analysts regularly perform work involving probabilistic assessments of reserve volumes, geologic scenarios, original volumes in place, and economic metrics that are associated with individual entities or multi-system projects. We are proud of our ability to report probabilistic work in a clear and concise format that is appreciated by technical and non-technical clients.

Litigation & Expert Testmony Support

Gruy professionals are experienced and available to provide litigation support. Senior staff members also arbitrate disputes in cases requiring the need for unbiased negotiation. The firm will represent its clients before state, federal, or international governmental agencies when required. We recognize the complexities and considerations particular to litigation and provide independent consulting tailored to meet those needs.

Fair Market Value Estimates

Our firm is distinguished by offering fair market value analysis of domestic and international holdings. We are often asked to estimate value attributable to producing assets, nonproducing properties, and mineral interests. Gruy value determinations are often selected for use in tax disputes, estate valuations, litigation, and equity transfers. For international valuation work, we provide an independent assessment of political risk.

Integrated Reservoir Studies

These studies are multi-disciplinary investigations involving geophysics, geology, petrophysics, plus reservoir and operations engineering. A single project may include a complete reservoir characterization followed by numerical simulations using black oil, compositional, or EOR models. The study often includes risk assessment, facility design, and economic evaluation. An integrated field study may provide field depletion plans.

Reservoir Characterization & Simulation

Our teams of engineers and geoscientists have the experience and knowledge to furnish complete reservoir descriptions. Through the expert application of geophysics, geology, petrophysics, and reservoir engineering, we can analyze and explain historical performance and forecast performance of hydrocarbon reservoirs. Geophysical interpretation, exploration geology, production geology, well log analysis, core analysis, and reservoir fluid modeling are all included. We have expertise in numerical reservoir simulation ranging from single well modeling to full field studies.

Deep Water Gulf of Mexico Fields

Gruy professionals have played a major role in the evaluation of deepwater discoveries in both the Gulf of Mexico and offshore Africa. Our work includes prospect analysis, reservoir studies including production forecasting, and probabilistic modeling of reserves and projected cash flows. We have been retained to perform large-scale reservoir analysis, and we have been hired by transportation companies to verify the magnitude of resources for pipeline economic decisions.

Rigorous Field and Site Inspection

Our engineers and geologists are qualified to perform rigorous site inspections to document equipment and conditions when needed for transaction records or verification. Our inspections include both pen and paper checklists and digital platforms. Equipment and special features are identified and logged via GPS and extensive photographic records, with facility condition and operational status noted. A complete report in booklet and digital format is generated for the stakeholder.

Our Professionals

Our professional engineers are licensed and all have over 25 years of industry experience completing complex and challenging assignments.




Our engineers possess considerable experience in applying reservoir and field analysis techniques, including the routinely applied performance trend extrapolations, material balance, and secondary recovery forecasting procedures. We apply these methods when other more extensive and time consuming approaches are not economically or technically justified. When needed, we use full-scale numerical reservoir simulation models, probabilistic models, and nodal analysis software to solve complex questions. Our engineers provide domain expertise to AI and Machine Learning practitioners solving reservoir performance forecasting challenges.



Geology and Geophysics

Our teams are experienced in detail oriented utilization and analysis of subsurface wellbore and seismic data from around the word. Dedication to excellence in our process results in accurate geological maps and precise volumetrics. To facilitate and optimize our methods, we maintain two popular geological mapping programs: GeoGraphix Exploration System (GES) and PETRA. Both programs use wellbore, well test, production, and seismic data in a variety of geoscience and engineering analysis tools to yield sound conclusions and superior presentations.



Production and Economic Data analysis

Our analysts collect and compile pertinent information to support practical, data-driven foundations for the approach we take in economic forecasting, analytical modeling and fair market value estimating. The goal is to arrive at reasonable conclusions by answering questions about historical industry activities and time-sensitive trends currently impacting the oil and gas business. The insights derived from those answers reflect both a high-level understanding of the business and the practical limitations that exist. The resulting judgments and business metrics are then applied to our client's forward looking projects.

Our 70 Years of Dedication and Excellence

At age 35, Hank Gruy founded H.J. Gruy and Associates, Inc. During his tenure as chairman of Gruy, he was active in professional associations at the international, national, and state levels.He was awarded the DeGolyer Distinguished Service Medal by the Society of Petroleum Engineers and the Lifetime Achievement Award from the Independent Petroleum Association of America. Among Hank’s industry achievements was serving as president of the Society of Petroleum Engineers (SPE) and serving as president of the Society of Petroleum Evaluation Engineers (SPEE). Hank was also recognized for Outstanding Achievements in the Field of Engineering by the Texas Society of Professional Engineers. He was a member of the National Academy of Engineering.

In 1996, the Gruy board of directors elected Marilyn Wilson as president of H.J. Gruy and Associates, Inc. Marilyn graduated from Texas A&M with a bachelor’s degree in petroleum engineering. She joined Gruy in 1982 following employment with a large pipeline company and a mid-sized independent E&P company.Marilyn served 6 years on the national board of the Society of Petroleum Evaluation Engineers, culminating in her election as president of the Society in 2002—the first woman to serve in that capacity. During her tenure on the board of SPEE, she was an active founding member of the SPEE/SEC Steering Committee from 2000-2003. This committee created the SPE/SEC joint forum attended by industry leaders from all categories of public and private E&P producers, and the engineering staff of the United States Securities and Exchange Commission (SEC). This forum created the gateway for the current dialogue between the public energy companies and the SEC regarding reserves reporting compliance and SEC definitions.

Prior to her very active role with SPEE, Marilyn was chairman of the board of directors of the Gulf Coast Section of SPE (1996-1997), chairman of the Houston Chapter of SPEE (1997-1998), and chairman of the Reservoir Study Group of SPEE (1990-1991). She also served on the board of the Women’s Energy Network from 1999-2001.

Marilyn is currently the CEO of H.J. Gruy and Associates, Inc. and has devoted her career to the advancement of professionalism in reservoir engineering.