This study reports the types of spelling errors made by the beginner learners of English in the EFL context as well as the major sources underpinning such errors in contextual writing composition tasks. Data were collected from written samples of 122 EFL students (male and female) enrolled in the intensive English language programme during the preparatory year at the University of Ha'il in Saudi Arabia. Students were given 1.5 hours to write on one of four different descriptive topics related to their life and culture. The spelling errors found in the writing samples was analysed and classified into four categories of errors according to Cook's Classification: omission, substitution, insertion, and transposition. An analysis of errors established that errors of omission constituted the highest proportion of errors. The majority of learners' spelling errors were related to a wrong use of vowels and pronunciation. When uncertain about accurate spellings, beginner learners often associated a wide range of vowel and consonant combinations in an attempt to spell words accurately, sometimes even combining two distinct lexical items by overlapping vowels. The findings suggest that spelling errors are mainly the outcome of anomalies existing in the target language of the learners as well as L1 interference from their internalized Arabic language system.