General Brazilian
compromisso forte / compromisso firme
Most commonly used in business and formal contexts
Rio de Janeiro
compromisso sério / compromisso de verdade
Colloquial usage emphasizes sincerity
São Paulo
compromisso firme / comprometimento forte
Often used in corporate and professional environments
Portugal
compromisso sólido / empenho firme
More formal; 'empenho' is preferred in European Portuguese