Electroanalytical stripping techniques have been well-used for trace-metal determinations, because of their remarkable sensitivity and selectivity. However, when these techniques are applied for organic materials, such as crude oil and petroleum-based fuels, the samples must be decomposed. This paper evaluates the use of different microwave ovens for the decomposition of crude oil and diesel fuel to determine the content of copper, lead, mercury, and zinc in the digestates. A focused-microwave (FM) oven using H2SO4/HNO3/H2O2, operated at atmospheric pressure, and a closed-vessel microwave (CVM) oven using HNO3/H2O2, operated under pressure in a vessel, were evaluated. Square-wave stripping voltammetry (SWSV) and stripping chronopotentiometry (SCP) at gold film electrodes were applied for copper, lead, and mercury. Potentiometric stripping analysis (PSA) at mercury film electrodes was applied for copper, lead, and zinc. SWSV was more affected by residual organic matter, especially for lead determination. SCP presented higher sensitivity for copper and mercury at gold electrodes. PSA at mercury electrodes was preferred for lead and zinc determination. Better detection limits were attained for FM-digested solutions, after 0.8-1.0 g of sample can be digested, in contrast to the low quantities (0.10-0.25 g) used when pressurized vessels were explored. Nevertheless, the loss of mercury was verified when samples were decomposed in the FM oven.