On July 18, 1952, respondent Juan Santos filed an application with the  Public  Service Commission (.Case No. 67556)  for a certificate of public convenience to operate a TPU-service on the line and territory of Adela  to Upper Mangyan via  San Jose  and  Mangarin,  Mindoro   (now Occidental  Mindoro), with the  use of 10 units.   The application was heard on November 5, 1952 with no opposition from any  one, and  at the hearing, respondent Santos testified that there were as yet no authorized operators on the  line applied for.   Nevertheless, no  action was  taken on the  application,  and it lay dormant until 1955.

Subsequently, on August 20, 1954,  petitioner  Fidel  del Rosario was granted  by the Commission in its  Case No. 79719 a certificate of public convenience valid for 25 years to operate  a TPU-service in Occidental Mindoro,  with the use of three unite on the line of Adela-Central-Camihauit and  vice-versa, and two units on the line Caminauit Pandurucan-Mangyan  and vice-versa.   Petitioner later filed another  application for authority  to operate additional trips along the same lines  with the  use  of  10 more units (Case No. 81392), which was approved by the Commission on November 20, 1954 for "7 auto  trucks only instead of 10,"  although  it found that  petitioner was "financially capable of  purchasing  the ten trucks applied for".

On July 19, 1955,  the  Commission rendered  judgment on the  1952  application of respondent Juan Santos  (Case No. 67556), granting him a certificate of public convenience to operate two auto-trucks along  the line Adela-Upper Mangyan via San Jose and Mangarin and vice-versa in Occidental  Mindoro for a period of  five years.   Learning of this  decision, petitioner Del Rosario filed  with  the Commission on August  15,  1955 a  motion for reconsideration thereof and  for reopening of  the  case to be given opportunity to oppose the application of Santos.  In said motion  for reconsideration, petitioner,  alleged that  his present  service of 12 units and 1 reserve along  the same lines applied for by Santos was sufficient,  adequate, and  Satisfactory; that  the authority given to  Santos  to operate 2 units along the same lines would result in ruinous competition to petitioner; and that the application of respondent Santos was granted without  notice to petitioner and on the basis of testimony given before  petitioner had been authorized to  operate a total  of 12  units on  the lines applied for  by Santos.  Petitioner Del Rosario  also opposed Santos 'petition  for  substitution of  his former  equipment which "were no longer serviceable" with new and  better equipment.

After hearing the arguments of both parties, the  Commission issued on September  19, 1955 an  order  denying  petitioner's  motion for reconsideration and reopening of  Case No. 67556 on the grounds that at the time the application of respondent Santos was filed, heard, and submitted, petitioner had not yet .been granted a certificate of  public convenience; that the Commission's decision granting the application of  respondent  Santos took into consideration its  own records regarding petitioner's service on the  same lines; and that the certificate granted to respondent Santos was only for five years, without extension of  line or increase of equipment or trips.   In the  same  order, the Commission granted Santos' petition for substitution of equipment.   From this order petitioner Fidel del  Rosario appealed to this court by petition for review.

Considering the radical change of conditions that occurred during the pendency of  the application of Santos,  after it was heard in 1952, due  to petitioner subsequent operation  of  his own  line,  and the need of  protecting established  operators and of avoiding  the cutthroat competition whenever possible, in order that the  service to the public may not suffer (Batangas Transportation Co. vs. Biñan Transportation supra,  p. 934),  we are of the opinion that the  petitioner should be given ample opportunity to substantiate his  objection against the  authority granted to  Santos.  While the Commission stated in order appealed from that it has taken into  account petitioner's service on the same lines, there may be relevant facts, though not on the record,  that  petitioner may  introduce in  evidence  and which the  Commission was not able  to consider  or to which it might have given the wrong emphasis.

The orders of July 9 and September 19, 1955,  appealed from are  hereby  set aside, and the records  ordered remanded  with instructions for the  Commission to reopen the proceedings and grant to the petitioner,  Fidel del Rosario, opportunity to be heard and  to substantiate his objections  against the proposed  service of respondent Juan Santos.  Cost against the latter.

Paras, C. J.,  Padilla,  Montemayor, Bautista  Angelo, Labrador,  Concepcion, Endencia  and  Felix, JJ.,  concur.