The NEXTflex-HT Barcodes are the largest set of single-index barcodes available for high-throughput Illumina sequencing. The NEXTflex-HT Barcodes each contain 12 nt unique index sequences with Hamming Distances of five or greater, permitting dual error correction to enable proper differentiation between samples by preventing ambiguity from PCR errors or sequencing instrument miscalling. Additionally, each pair of consecutive barcodes are fully color balanced and suitable for low level multiplexing.