The study of the representation and processing of grammatical gender during language production has encountered mixed results regarding which conditions must be met to observe gender effects and whether these reflect the selection of gender values or competition between elements of agreement. The answer seems to depend on the number of determiners associated to each gender and on the language being explored. The present study aims to assess this issue through three picture-word interference tasks in European Portuguese. This is a transparent Romance language featuring a one-to-one gender-determiner mapping system similar to opaque Germanic languages. Conditions of gender in/congruency between targets and distractors were considered along with gender transparency and agreement. We observed a gender congruency effect restricted to noun phrases. Importantly, the effect was modulated by transparency, which seems relevant regardless of agreement. To explain the results, we adapted the Dual-Route Model of language comprehension to production.