Efficient transmission resource allocation in medium access control (MAC) is essential for ensuring high performance in vehicular ad hoc networks (VANETs). However, existing solutions cannot satisfy the requirements of high throughput and low delay in high-density environments. In this article, we propose a timeslot-reserved MAC protocol to meet such demands for VANETs. This protocol provides distributed resource allocation and has two striking features: the high efficiency of handshake negotiation and the different solutions to disparate delay requirements of packets. In this protocol, a novel neighbor information table adds a new field of the needed number of frames in the future multiple frames. This reflects the reservation idea and reduces the number of negotiations between neighbor vehicles. The service applicant without enough timeslot resources is excluded from resource allocation negotiation, to decrease the invalid resource allocation. The resource-insufficient service channel and the resource-insufficient timeslot segments are also excluded from packet transmission, to further reduce the invalid resource allocation. Delay-sensitive packets and delay-tolerant packets select different kinds of timeslot segments, to satisfy different delay demands of different packets. Simulation results demonstrate the advantages of the proposed protocol in terms of throughput, delay, and packet loss rate.