This study attempts to investigate the production of English grammatical collocations amongst Saudi students majoring in English in the KSA and those in the UK. It also shows the most frequent types of errors that may occur as well as some possible reasons for their occurrence. For this purpose, the researcher analysed essays written by the participants. The results reveal that Saudi EFL learners in the UK do grammatical collocation errors less than those who learn English in the KSA. Additionally, the highest number of errors in both groups was recorded on the grammatical collocations patterns, noun + preposition and adjective + preposition. It seems that L1 interference plays a crucial role in students' erroneous responses, especially those which contain a preposition. For instance, the majority of noun + preposition, adjective + preposition and preposition + noun are used incorrectly throughout the essays. Furthermore, the avoidance phenomenon in SLA may be used by Saudi students. They tend to avoid using some grammatical collocation categories such as adjective + that- clause and noun + that-clause since they are beyond their English proficiency level. Finally, the lack of knowledge of grammatical collocations is another possible reason behind such errors. Educational leaders, curriculum designers and teachers need to shed light on these types, especially as the English language curricula used in the KSA do not pay a great deal of attention to grammatical collocations.