Entry · Price
CMO: Marginal operating cost
How much does it cost to serve one more unit of load?
Acronyms: PLD, Settlement Price for Differences (spot price); CCEE, Electric Energy Trading Chamber; ONS, National Electric System Operator.
In one sentence
Cost, per unit of energy produced, of meeting an increase of one unit of load in the interconnected system.
Real example
For the operating week identified by the ONS with the date Oct 2, 2026, the CMO published for the Southeast/Center-West was R$ 42.43/MWh (load levels light R$ 38.72, medium R$ 44.44 and heavy R$ 46.32)Nature of the data: Observed.
No Check this number record of its own in this example: the number comes from the panel's published database, which carries the source and the reference date.
Observed: Value published directly by the official or primary source.
Why it matters
How it is measured
In reais per unit of energy (shown as R$/MWh, as in the ONS definition, “custo, por unidade de energia produzida”; the ONS data dictionary records the unit of the weekly average as R$/MW), by subsystem and by load level (light, medium, heavy) in the weekly version. In the half-hourly version, the CMO of the subsystem is the average of the CMOs of the buses weighted by the loads.
Unit: R$/MWh, by subsystem; by load level in the weekly version
Not to be confused with
PLD (Spot price (Settlement Price for Differences))
The CMO is the cost of meeting one more unit of load, estimated by the ONS models by subsystem. The PLD starts from the CMO, but it is not the CMO: it is calculated by the CCEE by hour and submarket and applies the regulatory limits.
The CVU is a value of each thermal plant, considered in the Monthly Operation Program and in the models; the CMO is the cost of meeting one more unit of load, by subsystem. A plant's CVU is neither the CMO nor the PLD.
What cannot be concluded
- CMO is not PLD: the PLD applies regulatory limits and is calculated by the CCEE on an hourly basis.
Related entries
In the learning paths
See in the panel
Official source
ONSOpen data portal, dataset “CMO Semanal” (description and data dictionary)
Literal excerpt from the document
Portuguese only“Valores do custo, por unidade de energia produzida, para atender ao incremento de uma unidade de carga no SIN, chamado de Custo Marginal de Operação – CMO. Valores para cada semana operativa por subsistema, e por patamar de carga, além da média semanal, estimados pelo modelo Decomp.”
ONSOpen data portal, dataset “CMO Semi-Horário” (description and data dictionary)
Literal excerpt from the document
Portuguese only“Este CMO é estimado pelo modelo DESSEM para cada barra do sistema em base semi-horária. O CMO do subsistema é obtido pelo média dos CMOs nas barras de cada subsistema, ponderados pelas respectivas cargas [...]”
In other words: every day the CCEE calculates the prices for each hour of the following day, in each submarket, with three computer models, starting from the marginal operating cost and respecting a minimum limit and two maximum limits.
Literal excerpt from the document
Portuguese only“O Preço de Liquidação das Diferenças (PLD) é calculado pela Câmara de Comercialização de Energia Elétrica (CCEE) diariamente para cada hora do dia seguinte, considerando a aplicação dos limites máximos (horário e estrutural) e mínimo vigentes para cada período de apuração e para cada submercado. Este cálculo é realizado por modelos computacionais (Newave, Decomp e Dessem) e tem como base o Custo Marginal de Operação (CMO).”
Documents accessed and text checked on Sep 28, 2026.