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Guillaume Decaix

Offers broad strategic support to companies in the oil and gas sector, optimizing performance and finding sources of growth


Guillaume leads McKinsey’s office in Rio de Janeiro. He has been a resident of Rio since 2010, after relocating from the firm’s Benelux office. Guillaume also leads Petroleum Asset eXcellence (PAX) and our digital and advanced-analytics work within the oil and gas industry in Latin America, directing the efforts of specialized consultants, experts, and researchers.

Since joining McKinsey in 2004, Guillaume has honed his expertise in oil and gas, focusing on exploration and production strategy, deep offshore operations, mergers and acquisitions, and new market entry. He has supported a range of companies, including operators, oil-field-services providers, and equipment companies. He has also worked with metals and mining companies, advising executives on portfolio strategy, global commodity price dynamics, and mergers.

All of this advisory work has resulted in broad international experience with companies and teams in locations such as Belgium, Brazil, Colombia, Denmark, France, Germany, Italy, Luxembourg, Netherlands, Norway, Peru, Russia, South Africa, Sweden, and the United Kingdom.

Drawing on functional expertise in strategy, organization, and corporate finance, Guillaume has also worked on intense turnaround and restructuring efforts, bringing troubled companies back to stronger operating performance.

Examples of his recent client work include the following:

  • driving a major cost-reduction and restructuring effort for a floating production storage and offloading operator
  • developing breakthrough optimization of maintenance and productionbased on advanced analyticsfor a full FPSO
  • supporting a major Brazilian oil and gas company through a restructuring initiative following bankruptcy
  • supporting top-down due-diligence efforts for investors looking to make acquisitions in oil field services, equipment, and seismic services in Latin America
  • setting up an integration office for a merger affecting more than 300,000 employees, successfully capturing $6 billion in cost synergies in just six months

Before joining McKinsey, Guillaume worked in the automotive industry as an in-house consultant in sourcing strategy for Renault-Nissan. A native speaker of French, he is also fluent in English and Portuguese.

Published work

How Brazil can optimize its cost of energy,” McKinsey & Company, March 2021

Is there hidden treasure in the mining industry,” McKinsey & Company, November 2015

Hidden treasure? Low equity prices may offer important M&A opportunities for the mining industry,” McKinsey & Company, June 2015

Past experience

Internal consultant


French Institute of Petroleum, IFP School
MSc, engineering

MSc, electrical engineering