Disclosed are catalyst solutions for preparing aldehydes with variable normal- to iso-aldehyde ratios comprising one or more phosphonite ligands, rhodium, and a hydroformylation solvent. Also disclosed is a process for preparing aldehydes with variable normal- to iso-aldehyde ratios comprising contacting an olefin, hydrogen, and carbon monoxide with one or more phosphonite ligands, rhodium, and a hydroformylation solvent. The phosphonite-based catalyst solutions provide the ability to manipulate the normal- to iso-aldehyde ratio by varying one or more process variables including carbon monoxide partial pressure, temperature, and gram moles ligand to gram atoms rhodium.