As mentioned earlier, we successfully synthesized 401-mer and 399-mer oligos on CPG with reduced loading. Compared with results of that work, the present data are also much better. In the prior work, the bands corresponding to the full-length oligos after PCR amplification of the CBP purified oligos were weak (see Figure in the reference ) while the bands for the present work are strong (Figure ). The gel images of colony PCR results also provided evidence of superiority of the present work. For the prior work, according to gel images, plasmids from 23 out of 62 colonies could be readily determined not to contain the sequence of the synthetic oligo or to contain only a portion of it (see Figure in the reference ). For the present work, plasmids from 143 out of 144 colonies that were subjected to the analysis could be estimated to contain the expected sequence. For the prior work, a total of six plasmids that were determined to have the expected sequence based on the gel analysis were subjected to Sanger sequencing. Two sequences were correct, while the other four had at least one error. Later, we intentionally sequenced 14 additional plasmids that were predicted to contain only a portion of desired sequence according to electrophoresis results. We found that these sequences contained one or more blocks of deleted nucleotides. The deleted blocks ranged from 8 to over 100 nucleotides. For the 20 sequenced sequences, besides the block deletion errors, other errors include 11 single nucleotide deletions, and three G-to-A and one T-to-C substitutions. The error rates are not calculated because they do not make much sense due to the many deleted blocks of nucleotides. The sequencing data are included in the supporting information. Comparing those data with the present ones, it is evident that the major problem for synthesizing long oligos in pores of CPG and highly cross-linked polystyrene beads is block deletion and single deletion errors. In addition, the G-to-A substitution error is much easier to occur when the synthesis is conducted in pores because in the present work, not even a single Gto-A substitution occurred for all the 111 sequences sequenced. The comparison indicates that for long oligo synthesis, conducting the synthesis on smooth surface should be the choice.