For long oligo synthesis, besides the challenge of isolating the low percentage of full-length sequence from the crude mixture, another hurdle is errors in the target sequence, which include deletions, insertions and various substitutions. For the two 800-mer syntheses, the one synthesized on glass beads is significantly better in this aspect (Table ). For the entire synthesis, only two errors occurred. One was a single nucleotide deletion and the other was a 2-nt deletion. The total error rate was 0.0054%. The synthesis conducted on glass wool had more errors (Table ), and the total error rate was 0.0208%, which was about four times higher. The reason may be attributable to a less homogeneous reaction environment during automated synthesis for the case of glass wool. We did not cut glass wool to short segments because of the concern of generating small particles that could block the lines of the synthesizer. As a result, the glass wool was not freely movable in the synthesis column during reagent delivery. In contrast, the reaction environment for the case of glass beads is more homogeneous. For the synthesis results, it is remarkable that for the first 1,000-nt assembly for the 1,728-mer synthesis, only two errors were found for the 16 sequences that was sequenced (Table ). For the nucleotide beyond 1,000-nt, the error rate was slightly higher, but it was still far above our expectations. Compared with error rates reported in the literature using CPG as the solid support, the error rates in the present work were drastically lower (Table ). For example, among the most frequent substitution errors, which include G-to-A, G-to-T, C-to-T, T-to-C, and A-to-G (Entries 4-8), the highest G-to-A substitution was completely eliminated in all the three syntheses in the present work (Entry 4). For all other errors, the rates for the present work were consistently lower as well. The sum of the rates of substantial errors for the literature syntheses is 0.58%, while that for the present syntheses is less than 0.0434%, which is more than 10 times lower. It is noted that the numbers for the present work were from 800-mer and 1,728-mer synthesis, while the numbers from the literature was from the synthesis of oligos shorter than 100-mer. It is well known that error rates increase as oligos grow longer.