The wide-ranging energy and natural resources practice at CMS encompasses energy-related disputes and arbitrations, advice on the construction and purchase of facilities, and contracts work. The team supports clients across the renewables, wind, upstream oil and gas, and conventional energy industries. The group is led by three partners: Kostadin Sirleshtov has broad experience covering conventional, oil and gas, and nuclear energy; Dimitar Zwiatkow advises clients from the wind power, hydropower and photovoltaics field; and Borislava Piperkova, who was promoted to partner in April 2025, is an authority on renewables and carbon-free technologies.
Legal 500 Editorial commentary
Accolades
Client satisfaction: Lawyer & team quality
Testimonials
Collated independently by Legal 500 research team.
- 'Excellent client relationship management, responsiveness and accessibility, depth of team knowledge and international network. Excellent value for money and cost transparency.'
- 'Dimitar Zwiatkow and Konstantin Altandzhiyski demonstrate excellent understanding of our business and commercial awareness, excellent legal knowledge and ability in combination with innovative solutions.'
- 'The practice is unique in the way it combines technical expertise with a very practical, hands-on approach. The team is reliable, responsive, and focused on finding workable solutions, which makes them easy to engage with on complex matters.'
- 'Potential clients would value their ability to manage transactions smoothly under time pressure and to communicate clearly throughout the process. The team works in a collaborative way, both internally and with counterparties, which helps to avoid unnecessary delays.'
- 'The individuals I have worked with stand out for their availability, responsiveness, and clear communication. They are thorough, dependable, and provide advice that is both well considered and practical for decision-making. What I value most is their ability to remain calm under pressure and to keep matters moving forward efficiently. Dimitar Zwiatkow in particular has been very effective in coordinating matters and ensuring that deadlines are met.'
- 'They stand out for their responsiveness, willingness to support, and excellent knowledge of the regulatory environment.'
Key clients
- Toshiba International
- Rezolv Energy SA
- Shell Exploration and Production 96 B.V.
- OMV Offshore Bulgaria GmbH
- Renalfa IPP
- Aratiden
- Chint
- PPC
- Taaleri Energia Finnland
- United Bulgarian Bank
- DSK Bank
Work highlights
Advised Toshiba International on a procurement contract with Bulgaria’s National Electricity Company for the rehabilitation of the 864MW Chaira Pumped Storage Hydropower Plant.
Advised Rezolv Energy on the €90m financing and development of the 229 MW “St. George” solar park in Bulgaria, including VPPA, EPC, and sustainability-linked aspects.
Advising the lender, DSK Bank, on the €58.5m financing to for the development of a PV plant, with a total capacity of 40 MW and BESS (93 MW/h).
Lawyers
Leading partners
The strongest partners in their field, leading on market-leading deals and endorsed by peers and clients alike.
Next Generation Partners
Junior partners with significant recognition from clients and peers in the market and key roles on multiple matters.
Practice head
Kostadin Sirleshtov; Dimitar Zwiatkow; Borislava Piperkova
Other key lawyers
Diyan Georgiev