In this paper, we propose Spacing-based Channel Occupancy Regulation (SCORE) MAC protocol that provides proportional service differentiation in terms of normalized throughput in wireless LANs. As shown by our system model and simulation study, SCORE provides consistent, scalable and adjustable proportional differentiation for any network size, any service class distribution, any node data rate and any packet size. Compared to state-of-the-art prioritized service differentiation schemes like Enhanced Distributed Coordination Function, SCORE can quantitatively control the channel sharing between different service classes with significant performance gain in terms of higher network throughput and lower packet collision probability. Categories and Subject Descriptors C.2.1 [Network Architecture and Design] Wireless communication; C.2.5 [Local and Wide-Area Networks] Access schemes General Terms Algorithms, Design, Performance Keywords Wireless LANs, Medium Access Control, Proportional Ser...